An Improved Valve Mechanism For Regulating Flow

TECHNICAL FIELD The present disclosure relates to a valve mechanism for regulating flow in a pipe line. Particularly, the present disclosure relates to a valve mechanism for creating a bypass for the flow when a pipe line, conveying fluid/semi-solid material, is under maintenance or is non-functional. BACKGROUND OF THE PRESENT DISCLOSURE The information in this section merely provides background information related to the present disclosure and may not constitute prior art(s). Generally pipelines for waste flow are provided with a valve mechanism to regulate and control the waste flow through the pipeline. More specifically, valve mechanisms are used to bypass the waste flow when a main flow line (also referred to as P-trap hereinafter), through which the waste flows under normal conditions, is nonfunctional due to jamming/clogging or is under maintenance. Conventionally, the P-trap, such as in case of toilet systems in locomotives, is connected to the main flow pipeline and is normally used for the outflow of waste from the main pipeline. Under certain conditions when the P-trap is jammed due to litter or other solid matter getting stuck, the P-trap is bypassed by means of a valve connected directly to the main flow pipeline to expel the litter or solid matter from the system. For such purpose, a Quarter Turn Ball valve is employed. A ball valve comprises a valve-housing, a valve-ball in the housing that can be turned between an open and a closed condition, pipe connectors connected to opposite ends of the housing, and valve seats located within the housing and resiliently urged into sealing engagement with the ball. O-ring seals are provided between the valve seats and the inside periphery walls of said recesses in the adaptors, and the valve seats carry non-metallic, for example polymers (such as nylon, Teflon etc.), sealing rings in engagement with the ball. The ball valve provides are leak proofing and can be opened/closed quickly. Therefore, when the operator actuates the valve to open it, the 3 ball moves/turns about a closed condition to allow the accumulated waste to pass through the valve. One major problem associated with the existing Quarter Turn Ball Valve is that it has a faulty actuation mechanism. Opening/closing the ball valve due to a number of mechanical components is cumbersome and sometimes results in the actuation system getting jammed or stuck frequently. Further, area of contact between the valve-ball and interior of valve-housing with which the valve ball remains in contact is more. With permeation of semi-solid waste between clearances of the valve-ball and the valve-housing, the force required to operate the ball valve increases significantly. This in turn results in a decreased credibility of the ball valve mechanism for the purpose of cleaning/maintenance of the waste flow pipeline. In other words, researchers have developed a user friendly and technically advance valve mechanism for regulating flow in a pipe line. More specifically, in light of foregoing discussion, it is necessary to develop an improved valve mechanism for regulating flow in a pipe line to overcome one or more limitations stated above. SUMMARY One or more drawbacks of conventional valve mechanism as described in the prior art are overcome and additional advantages are provided through the improved valve mechanism as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure. In one non-limiting embodiment of the present disclosure, there is provided an improved valve mechanism for regulating flow in a pipeline. The improved valve mechanism comprises a valve unit and a drive unit; the valve unit comprising an adapter plate, a top plate and housing; and a passage extending through the adapter plate, top plate and the housing. The valve mechanism also comprises a slide plate adapted to be received in the housing and being movable between a closed condition and an open condition of the valve unit wherein the closed condition is defined as the 4 position in which the passage is completely covered by the slide plate; and the open condition is defined as the position in which slide plate is completely removed from the passage. The valve mechanism further comprises a drive mechanism for sliding the slide plate between open condition and closed condition of the valve unit. In an embodiment of the present disclosure, the adapter plate comprises a first upper face, a first lower face and a first hole; the first upper face is being connected to a Ptrap of a pipe line; and the first lower face is being connected to a second upper face of the top plate. In another embodiment of the present disclosure, the top plate comprises second upper face, second lower face and second hole; the second upper face being connected with the first lower face of the adapter plate; and the second lower face is connected to the third upper face of the housing. In a further embodiment of the present disclosure, the adapter plate, the top plate and the housing each comprise a hole that defines the passage for flow when the holes of the top plate, bottom plate and housing are aligned. In one more embodiment of the disclosure, the slide plate is received movably in guide seals mounted along sides of the housing. In a still further embodiment of the present disclosure, the slide plate comprises a proximal end and a distal end; the proximal end being adapted to open/close the passage for waste flow from the main flow pipe to the retention tank; and the distal end being configured with a drive unit for slidably moving the slide plate during actuation of the valve mechanism. It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure. The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described 5 above, further aspects, embodiments, and features will become apparent with reference to the drawings and the following detailed description. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The novel features and characteristics of the disclosure are set forth in the appended description. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which: Figure 1 shows a perspective view of the existing Quarter Turn Ball valve mechanism used in waste flow pipelines. Figure 2 illustrates the present valve mechanism for use waste flow pipelines in an embodiment of present disclosure. Figure 3 shows an exploded view of the various sub-parts and sub-assemblies that are contained in the present valve mechanism according to one more embodiment of present disclosure. Figure 4 depicts an isometric view of the valve mechanism according another embodiment of present disclosure. Figure 5 depicts a sectional view of the slide plate and locking wedge of the housing in an open condition of the valve unit according to the above described embodiment of the present disclosure. Figure 6 depicts a sectional view of the slide plate and locking wedge in closed condition of the valve unit according to the above described embodiment of the present disclosure. 6 Figure 7 depicts a sectional view of the guide seal and the slide plate according to another embodiment of the present disclosure. Figure 8 depicts an isometric view of the valve unit in closed condition according to another embodiment of the present disclosure. Figure 9 shows an isometric view of the valve unit in partially open condition according to yet another embodiment of the present disclosure. Figure 10 illustrates the valve unit in completely open condition according to one more embodiment of the present disclosure. Figure 11 depicts an alternate embodiment of the present disclosure whereby the valve unit is in closed condition. Figure 12 shows the alternate embodiment of the present disclosure whereby the valve unit is in an intermediate condition. Figure 13 illustrates the alternate embodiment of the present disclosure whereby the valve unit is in open condition. The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the assemblies and methods illustrated herein may be employed without departing from the principles of the disclosure described herein. DETAILED DESCRIPTION While the invention is subject to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figures and will be described below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the spirit and scope of the invention as defined by the appended claims. 7 Before describing in detail the various embodiments of the present disclosure it may be observed that the novelty and inventive step that are in accordance with the present disclosure resides in a valve mechanism for regulating flow in a pipeline. It is to be noted that a person skilled in the art can be motivated from the present disclosure and can perform various modifications. However, such modifications should be construed within the scope of the invention. Accordingly, the drawings are showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein. The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that an assembly, setup, system, device that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system or device or setup. In other words, one or more elements in the system or apparatus or device proceeded by “comprises a” does not, without more constraints, preclude the existence of other elements or additional elements in the assembly or system or apparatus. The following paragraphs explain present disclosure. The invention in respect of the same may be deduced accordingly. Accordingly, it is an aim of the present disclosure to provide a toilet system for locomotives such as trains. Another aim of the present disclosure is to provide a valve mechanism for regulating flow in waste flow pipelines. One more aim of the present disclosure is to provide a valve mechanism that overcomes or at least reduces the problem of jamming of the valve. Accordingly, the present disclosure provides a valve mechanism for regulating flow through a pipe line; the valve mechanism comprising a valve unit and a drive unit; the valve unit comprising an adapter plate, a top plate and housing; and a passage extending through the adapter plate, top plate and the housing. The valve mechanism also comprises a slide plate adapted to be received in the housing and being movable 8 between a closed condition and an open condition of the valve unit wherein the closed condition is defined as the position in which the passage is completely covered by the slide plate; and the open condition is defined as the position in which slide plate is completely removed from the passage. The valve mechanism further comprises a drive mechanism for sliding the slide plate between open condition and closed condition of the valve unit. In an embodiment of the present disclosure, the adapter plate comprises a first upper face, a first lower face and a first hole; the first upper face is being connected to a Ptrap of a main pipe line; and the first lower face is being connected to a second upper face of the top plate. In another embodiment of the present disclosure, the top plate comprises second upper face, second lower face and second hole; the second upper face being connected with the first lower face of the adapter plate; and the second lower face is connected to the third upper face of the housing. In a further embodiment of the present disclosure, the adapter plate, the top plate and the housing each comprise a hole that defines the passage for flow when the holes of the top plate, bottom plate and housing are aligned. In yet another embodiment of the present disclosure, the slide plate is received movably in the guide seals of the housing. In one more embodiment of the present disclosure, the peripheral edge of the housing comprises a locking wedge having a slant side. In another embodiment of the present disclosure, the slide plate comprises a proximal end and a distal end; the proximal end being adapted to open/close the passage for waste flow from the main flow pipe to the retention tank; the distal end being configured with a drive unit for slidably moving the slide plate during actuation of the valve mechanism; and the peripheral side comprising a tapered portion. 9 In one further embodiment of the present disclosure, in the closed condition of the valve unit, the tapered portion of the peripheral side of the slide plate forms mating contact with the slant side of the locking wedge. Accordingly the present disclosure provides a toilet system comprising a main flow pipe being connected with a retention tank through a secondary flow pipe by means of a P-trap; and a waste disposal tank being connected with the main flow pipe by means of a valve mechanism; wherein the valve mechanism is configured to allow flow from the main flow pipe to the secondary flow pipe through the P-trap to the retention tank in the closed condition of the valve unit; and the valve mechanism being configured to allow flow from the main flow pipe to the waste disposal tank by bypassing the P-trap in the open condition of the valve unit. Reference will now be made to a valve mechanism and is explained with the help of figures. The figures are for the purpose of illustration only and should not be construed as limitations on the assembly and mechanism of the present disclosure. Wherever possible, referral numerals will be used to refer to the same or like parts. Figure 2 is an exemplary embodiment of the present disclosure which illustrates a perspective view of a toilet system comprising a main flow pipe (M) being connected with the retention tank through a secondary flow pipe (N) by means of a P-trap; and to a waste disposal tank by means of a valve mechanism. The valve mechanism comprises a valve unit (VU) and a drive unit (DU) wherein the valve unit (VU) is mounted with the main pipe line (M) to regulate the flow there through. In the mounted condition, valve mechanism is configured to allow flow from the main flow pipe (M) to the retention tank through secondary flow pipe (N) through the P-trap in the closed condition of the valve unit; and the valve mechanism being configured to allow flow from the main flow pipe (M) to the waste disposal tank by bypassing the P-trap in the open condition of the valve unit. As shown in figures 3 and 4, the valve unit (VU) comprises an adapter plate (1) having a first upper face (1a); a first lower face (1b) and a first hole (1c). The valve unit (VU) further comprises a top plate (2) corresponding to the top plate (2). The top 10 plate (2) has a second top face (2a), a second bottom face (2b) and a second hole (2c). In the assembled condition of the valve unit (VU), the top plate (2) is disposed between the adapter plate (1) and housing (3). The housing (3) comprises a third upper face (3a), a third lower face (3b) and a hole (3c). In the assembled condition, the first upper face (1a) of the adapter plate (1) is connected to the P-trap of a main pipe line (M) and the first lower face (1b) is connected with the second upper face (2a) of the top plate (2). The third upper face (3a) of the housing (3) is connected with the second lower face (2b) of the top plate (2) and the third lower face (3b) of the housing (3) is being connected to a retention tank. The valve unit (VU) further comprises a three seals; a round seal (S1) being disposed between the first lower face (1b) of the adapter plate (1) and second upper face (2a) of the top plate (2); two wiper seals (S2), one being disposed between the second lower face (2b) of the top plate (2) and an upper face of the slide plate and the other disposed between a lower face of the slider plate and third upper face (3a) of the housing (3); and two guide seals (S3) being fixed on the housing (3) thereby providing sealing against leakage. The valve unit (VU) is mounted with the main pipe line to regulate the flow there through. The top plate (2), the housing (3) and the bottom plate (2) are mounted such that the first hole (1c), the second hole (2c) and the third hole (3c) are aligned so as to define a passage (P) for the flow of a semi-solid/liquid substance such that the passage of the valve unit (VU) is aligned with the main pipe and an opening to the waste disposal tank. As shown in figures 5-7, the housing (3) comprises a plurality of sides (S), defined internally along the peripheral edges (3d). A slide plate (4) is received movably in the housing (3) such that the slide plate (4) is slidable in the guide seal (S3) mounted along the sides (S) in the housing. In other words, peripheral sides (4d) & (4e) of the slide plate (4) is supported in the guide seals mounted in the housing (3); the first peripheral side (4c) having first tapered portion (T1) and second peripheral sides (4d) & (4e) having second tapered portion (T2). In an embodiment of the present disclosure, the sides (S) are provided with guide seals (S3) made of a polymeric material such Teflon etc., for avoiding metal to metal contact during sliding motion of the slide plate (4); thereby leading to decreased friction during sliding of the slide plate (4) eventually resulting in less mechanical force required to slide the same. A locking wedge (W) is formed on the peripheral edge of the housing (3d); the locking 11 wedge (W) having a slant side (WS). The gradient of the slant side (WS) is corresponding to the gradient of first tapered portion (T1) of the slide plate (4) such that in the closed condition of the valve unit (VU), the first tapered portion (T1) of the first peripheral side (4c) of the slide plate (4) forms mating contact with the slant side (WS) of the locking wedge (W). The slide plate is capable of sliding linearly along the length (L) of sides (S) of the housing (3). The slide plate comprises a proximal end (4a) and distal end (4b). In the mounted position, the slide plate (4) is received in the housing (3) such that the proximal end (4a) of the slide plate (4) slides between the second lower face (2b) and third upper face (3a) so as to open/close the third hole (3c); thereby resulting in opening/closing of the passage (P) for waste flow thus regulating the flow of waste directly from the main flow pipe (M) to the waste disposal tank i.e. by by-passing the P-trap. During the sliding motion of the slide plate (4), entry of unwanted waste into the valve unit (VU) is prevented by the round seal (S1) provided between the second upper face (2a) and the first lower face (1b). In the closed condition, the slide plate (4) is locked in place with the locking wedge (W) in the housing (3). During movement of the slide plate (4) from the open condition of the valve unit (VU) to the closed condition, the first tapered portion (T1) of the first peripheral side (4c) of the slide plate (4) lifts the round seal (S1) in the upward direction towards the adapter plate (1). The upward movement of the round seal (S1) in turn leads to compression of the ORing (10); thereby creating a positive seal pressure between the slide plate (4) and the round seal (S1), which stops any waste from leaking into the valve unit (VU) in the closed condition. The distal end (4b) of the slide plate (4) is adapted to be coupled with the drive unit (DU) for sliding/moving the slide plate (4) when an actuation force is applied. The drive unit (DU) comprises a rack (6) which is rigidly secured with the distal end (4b) of the slide plate (4) and comprises a plurality of teeth for operatively engaging with a pinion (5). The pinion (5) is mounted on a drive shaft (7) and is rotatable with the rotation of the drive shaft (7); the drive shaft (7) being coupled with an operating means such as a pulley, electric motor, etc. In an embodiment of the present disclosure, two bearings (9) are mounted on both sides of the pinion (5) to ensure that the pinion (5) has rotary motion only in a direction parallel to the rack. Collar (8) 12 restricts the longitudinal movement of the pinion (5) during operation of the drive unit thereby enhancing accuracy during actuation. According to a still further embodiment of the present disclosure, as shown in figures 8-10, the drive unit (DU) is rotated by means of a pulley (15) which is mounted on the drive shaft. The pulley (15) can be rotatable by means of a rope, wire etc. As shown in figure 8, in closed condition of the valve unit the proximal end of the slide plate (4) covers the hole (3c) of the housing (3) thereby obstructing the passage (P) for the flow of waste. Thus, in the closed condition of the valve unit, waste passes from main pipe line to retention tank through the secondary pipe line (N) and through the P-Trap. Under unwanted circumstances such as blockage/maintenance of P-trap, when the user actuates the pulley (15) by means of a rope, wire or any other actuation medium, the shaft (7) starts rotating. The rotation of the shaft (7) leads to the rotation of the pinion (5) in the direction of rotation of the pulley. This results in actuation of the rack in a linear direction. This movement leads to a movement of the slide plate (4) in the guide seals (S3) present in the housing (3) such that the proximal end (4a) slides towards the pinion (5). This leads to opening of the passage for the flow of litter/waste through the valve unit. Figure 9 depicts an intermediate position when the valve unit is opening from a closed condition. On further rotation of the pulley, the proximal end (4a) of the slide plate (4) moves towards the pinion (5) until the passage (P) of the is completely open for passage of waste i.e. open condition of the valve unit as shown in figure 10. In an alternate embodiment of the present disclosure, as shown in figures 11-13, the drive unit (DU) is actuated by a scotch yoke mechanism. The scotch yoke mechanism comprises a crank (11), crankshaft (12) and a sliding actuator (13) being configured with the crankshaft (12). An actuation slot (14), extending in the lateral direction, is provided at the distal end of the slide plate. The term ‘lateral direction’ herein refers to a direction perpendicular to the direction of sliding motion of the slide plate, in the plane of the slide plate. Accordingly, a slot is provided on the top plate to accommodate the positions of the sliding actuator (13), in the open and closed conditions of the valve unit (VU). During actuation of the drive unit (DU), the crankshaft (12) rotates thereby causing actuation of pulley. The pulley has the same actuation mechanism for rotation as the rack and pinion mechanism. The crankshaft 13 (12) is also configured to a bearing which enables full transfer of torque from the pulley to the crankshaft during actuation of the valve unit (VU). In the open condition of the valve unit (VU), the slide plate stops at the end of the housing, thereby eliminating the need of an open side in the housing to accommodate the distal end of the slide plate (as shown in figure 13). In one further embodiment of the present disclosure, the present valve mechanism can be used for waste systems in toilets installed in locomotives such as buses and railway coaches. In such an application, the valve mechanism can be automated using the electrical/pneumatic system of the railway coaches thereby allowing a remote user to actuate the drive unit (DU) of the valve mechanism. In other applications, the present valve mechanism can be used in waste digesters in housing societies, portable toilets etc. List of reference numerals: 1 Adapter Plate 1a First Upper Face 1b First Lower Face 1c First Hole 2 Top Plate 2a Second Upper Face 2b Second Lower Face 2c Second Hole 3 Housing 3a Third Upper Face 3b Third Lower Face 3c Third Hole 3d Peripheral edges of the Housing 4 Slide Plate 4a Proximal End of Slide Plate 4b Distal End of Slide Plate 4c First Peripheral side of the Slide Plate 4d,4e Second Peripheral sides of the Slide Plate 5 Pinion 6 Rack 14 7 Drive Shaft 8 Collar 9 Bearing 10 O-Ring 11 Crank 12 Crankshaft 13 Sliding Actuator 14 Actuation Slot 15 Pulley M Main Pipe line N Secondary Pipe line P Passage S Side of the Housing T1 First tapered portion T2 Second tapered portion W Locking Wedge S1 Round Seal S2 Wiper Seal S3 Guide Seal DU Drive Unit VU Valve Unit WS Slant Side Equivalents: With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “having” should be interpreted as “having at least,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim 15 recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

We claim: 1. A valve mechanism for regulating flow through a pipe line; the valve mechanism comprising a valve unit (VU) and a drive unit (DU); the valve unit (VU) comprising: an adapter plate (1); a top plate (2); a housing (3); a passage (P) extending through the adapter plate (1), top plate (2), and the housing (3); a slide plate (4) adapted to be received in the housing (3) and being movable between a closed condition and an open condition of the valve unit (VU) wherein the closed condition is defined as the condition in which the passage (P) is covered by the slide plate (4); and the open condition is defined as the condition in which slide plate (4) is removed from the passage (P); a drive mechanism (DU) for actuating the slide plate (4) between open condition and closed condition of the valve unit. 2. The valve mechanism as claimed in claim 1, wherein the adapter plate (1) comprises a first upper face (1a), a first lower face (1b) and a first hole (1c); the first upper face (1a) is being connected to a P-trap of a main pipe line (M); and the first lower face (1b) is being connected to a second upper face (2a) of the top plate (2). 3. The valve mechanism as claimed in claim 1, wherein the top plate (2) comprises second upper face (2a), second lower face (2b) and second hole (2c); the second upper face (2a) being connected with the first lower face (1a) of the adapter plate (1); and 17 the second lower face (2b) is connected to third upper face (3a) of the housing (3). 4. The valve mechanism as claimed in claim 1, wherein the adapter plate (1), top plate (2), and the housing (3) each comprise holes (1c), (2c) and (3c) that defines a passage (P) for flow when the holes of the adapter plate, top plate and housing are aligned. 5. The valve mechanism as claimed in claim 1, wherein the slide plate (4) is received movably in guide seals (S3) mounted along sides (S) of the housing (3). 6. The valve mechanism as claimed in claim 1, wherein the peripheral edge (3d) of the housing (3) comprises a locking wedge (W) having a slant side (WS). 7. The valve mechanism as claimed in claim 1, wherein the slide plate (4) comprises a proximal end (4a), a distal end (4b), first peripheral side (4c) and second peripheral sides (4d) & (4e); the proximal end (4a) being adapted to open/close the passage (P) for waste flow from the main flow pipe to the retention tank; the distal end (4b) being configured with a drive unit (DU) for slidably moving the slide plate (4) during actuation of the valve mechanism; and the first peripheral side (4c) having first tapered portion (T1) and second peripheral sides (4d) & (4e) having second tapered portion (T2). 8. The valve mechanism as claimed in claim 1, wherein in the closed condition of the valve unit (VU), the first tapered portion (T1) of the slide plate (4) forms mating contact with the slant side (WS) of the locking wedge (W). 9. A toilet system comprising a main flow pipe (M) being connected with a retention tank through secondary flow pipe (N) by means of a P-trap; and a waste disposal tank being connected with the main flow pipe by means of a 18 valve mechanism; wherein the valve mechanism is configured to allow flow from the main flow pipe (M) to the retention tank to the secondary flow pipe (N) through the P-trap in the closed condition of the valve unit; and the valve mechanism being configured to allow flow from the main flow pipe (M) to the waste disposal tank by bypassing the P-trap in the open condition of the valve unit.