Everything you need to know about Plumbing



(i) Two pipe system:

Soil fixture such as urinals & water closets connected to vertical soil pipe. The connection of waste matter from baths, kitchens etc., are made to another vertical waste pipe.

(ii) One pipe system partially ventilated:

There is one soil pipe & all the waste matter from waster closets, baths, sinks etc., is discharged in this pipe. Then is also vent pipe which provide ventilation only to the traps or water closets.

It has separate stacks for carrying sewage and waste water.

(i) Two pipe system

(a) Soil Stack:

Fixtures human excreta urinal obnoxious waste connected to a separate stack known as soil stack which is directly connected to a sewer unit through a man hole. Each fixture connected to the soil pipe must be provided with a trap.

(b) Antisiphonage pipe:

When fixtures are connected on top of tall buildings high rate of flow from water closet from upper floors may induce negative pressure & induce siphonage. When the flow passes the fixture to lower floors resulting in loss of trap seal. This can be prevented by connecting the crown of the trap to a separate stack which terminates a roof level.

Traps on all floors are connected to this pipe. The stack called the anti siphonage pipe provides access to atmospheric air, eliminating the possibility of generating negative pressure, there by maintaining hydraulic equi­librium in the system.

(c) Waste Stack:

Ablutionary fittings used for washing and cleanup, e.g. wash basins, bath tubs, showers, drinking water fountains, kitchen sinks and water from air condi­tioning machines, etc. are connected to a separate stack. Many of these fixtures do not have their own traps but may discharge over a floor trap within a bathroom or kitchen.


(a) It ensures segregation of the foul sewage from waste water.

(b) There is no danger of backflow of sewage in waste fitting in case of blockage of the soil pipe.

(c) The system enables use of the separated waste water directly for irrigation and gardening where so possible.

(d) The separate waste stack permits arrest of solids from kitchen in the gully traps however need is to be cleaned manually once in a while.


(a) Difficult to install in high rise buildings where the vertical stacks terminate in a service floor or in the ceiling of a basement.

(b) Long horizontal runs are required to reach the external wall and the lines connected to the sewer. Provision of the gully trap becomes quite difficult in these situations.

(c) The two pipe system with the third anti-siphonage pipe requires more space in vertical shaft and in horizontal runs and proves costlier than the other systems.

Two pipe systems have been largely replaced by one pipe and single stack systems.

(i) One pipe system partially ventilated:

A separate Vent pipe is added.

Basic system:

This system eliminates the waste slack and the gully trap required in the two pipe system.

(a) Soil and Waste Stack:

All fixtures carrying human excreta or abolitionary waste are connected to a single vertical stack. Each fixture is provided with a trap having a minimum seal of 50 mm for waste and 75 mm for soil appliances.

(b) Anti-Siphonage Stack:

This stack is similar to one described for two pipe system. However, all traps in the waste fixtures must also be connected to it in addition to the trap of soil fixtures.

One pipe system is now used in all modern buildings. High quality pipes, fittings and installation techniques aided by constant flow of water from soil or waste fittings ensure reduction of blockage problem.

Elimination of gully traps reduces need for manual cleaning. Providing gully traps in service floors or base­ments in high rise building has proved difficult and unpractical.

The system having one pipe requires lesser space in pipe shafts and ducts.

It is important that the length and slope of connections from the branch lines to a stack should have a long radius bend at the foot of each stack and the ground floor connections be made directly to the manhole.

Single Stack System:

Basic System:

Single stack system eliminates the anti-siphonage pipe in the one pipe system.

Suggested pipe system for different types of buildings:-

(i) One or two storeyed building two pipe system, one pipe system, and single stake.

(ii) 3 to 4 storeyed out pipe system single stack system.

Multistory one pipe system.

A single Vertical solid pipe is fixed & all the waste matter from bath, kitchen water closets etc. is discharged in to it partially. Ventilated single stack system.