What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
Same word, different thingsoil and vent pipe (SVP)
also soil stack, waste pipe, above-ground drainage
British practice separates SOIL (from WCs) from WASTE (from basins, baths, sinks) as distinct terms — so "waste" excludes sewage rather than including it.
Australia
Close, not identicalsanitary plumbing
also soil stack, waste, stack
Australian practice keeps the soil-and-waste distinction in its terminology but groups both under sanitary plumbing, with its own venting rules.
United Statesyours
Same word, different thingDWV
also drain-waste-vent, soil stack, waste line
DWV bundles all of it into one system name, and American "waste" commonly covers everything including sewage — the opposite of the narrower British sense.
Canada
Same word, different thingDWV
also drain-waste-vent, sanitary drainage
As the United States for the terminology, with Canadian venting provisions differing in detail — so the words map and the permitted arrangements do not.
The governing standard, by market
United Kingdom
BS EN 12056-2
Sanitary pipework — layout, calculation and venting.
United States
IPC / UPC
Drainage fixture units, pipe sizing and venting requirements.
Australia
AS/NZS 3500.2
Sanitary plumbing and drainage.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Does waste mean the same thing everywhere?
- No, and the British sense is narrower than the American one. In British practice SOIL is the discharge from WCs and urinals, and WASTE is the discharge from basins, baths, showers and sinks — two named categories with different pipe sizes, different gradients and historically different routes. In American practice the drain-waste-vent system names everything together and "waste line" commonly covers all of it. So a British specification calling for a waste pipe is describing something that does not carry sewage, and reading it with the American sense will size the wrong pipe and route it to the wrong place.
- What is the vent actually for?
- Keeping the water seals in the traps intact, which is what stops drain air entering the building. Every fixture has a trap holding a small depth of water, and that seal can be broken two ways: a discharge running past the trap can siphon the water out, and a surge elsewhere can push the water back through it. A vent path connected to the system equalises the pressure on both sides of the seal, so neither happens. Every market requires venting and all of them permit several arrangements — a full vent stack, individual vents, air admittance valves where the code allows them — and the permitted arrangements differ, so a layout valid in one jurisdiction may not be in another.
- Why is the fall of a drain a specified range rather than a minimum?
- Because too much fall is a defect as well as too little. A pipe laid too shallow does not develop enough velocity to carry solids and silts up; a pipe laid too steep lets the water run away from the solids, which are left behind and build up — the same blockage from the opposite cause. So codes give a gradient range for each pipe size, and the correct answer is within it rather than as steep as the site allows. The related trap is a pipe laid to a nominal gradient over a long run without checking intermediate levels, which produces a series of shallow and steep sections averaging correctly and behaving as neither.