This is the best and most improved system of plumbing. Two sets of vertical pipes, one for excreta (night soil) as soil pipe and another for sullage as waste pipe. The soil pipes as well as waste pipes are separately ventilated, by providing, separate vent pipe or anti-siphon age pipe. This system has four vertical pipes.
Instead of using two separate pipes for excreta and sullage, only one vertical main pipe is provided, which collects both night soil and sullage water. The main pipe is ventilated at the top, in addition, a separate vent pipe is also provided. This system has two vertical pipes
This system is having a single pipe for soil, waste and vent without any separate ventilation pipe. It uses only one pipe, which carries night soil as well as sullage and the same pipe is extended up to 2 m above roof level with a cowl to act as vent pipe for removal of gases.
This is an improved form of single stack system, where the traps of the water closets are ventilated, by a separate vent pipe, called relief vent pipe. This system uses two pipes as in single pipe system. The single soil and waste pipe is connected to vent pipe and thus cost is reduced.
The ventilation is usually achieved by providing a fresh air inlet connected to the lower-most manhole or inspection chamber. Fresh air from the atmosphere will enter through this inlet into the manhole, and finally goes out at top through the vent pipe. The air along with foul gases will finally escape out from the cowl provided at the top. A flap valve is provided at the inlet of fresh air into the inspection chamber, to avoid the escape of foul gases in the street or courtyard.
Water seals of traps in multi storied building may some times get broken due to siphonic action. When wastewater is suddenly discharged from a sanitary fixture on the upper floor, it moves rapidly through the soil (waste) pipe, it may suck some air from the lateral pipe connecting the soil pipe with fixtures at lower floor. This sucked air causes siphonic action, resulting in the flow of water from the trap of the fixture to the soil pipe and thus breaking its water seal.
To overcome this difficulty, a separate pipe of smaller diameter is attached to the traps, which connects the trap to the vent pipe. This pipe is known as anti-siphonage pipe and it supplies air to the short branch pipe of the lower fixture, at the time of suction, otherwise it acts as a vent pipe of the lower fixtures. This pipe normally serve as vent pipe and as anti-siphonage pipe in case suction takes place.
All house sewer connections with any municipal (street) sewer 300 mm or smaller in size shall be made by means of wye or tee branches or other special fitting provided in such sewer for that purpose. The house sewer shall be connected to municipal sewer at an existing wye, tee, stub or riser provided.
Each service connection shall be laid in a separate private trench on a straight line and gradient from the Wye to the end of the service connection at the property line. No service connection shall be laid on a grade of less than two percent (1 in 50).
Interceptors (including grease, oil and sand interceptors, etc.) shall be provided for the proper handling of liquid waste containing grease, flammable waste, sand and any other ingredients that could be harmful to the building drainage system, the public sewer or processes involved in the treatment of sewage at the sewage treatment plant.
In a building in which the whole or part of the plumbing system lies below the house connection to the public sewer, the outlet from said plumbing system or part thereof shall discharge into a sump or receiving tank from which the sewage shall be pumped through a pipe to the manhole in the house sewer connection or to the public sewer.