Sanitary Drainage, Sewerage, and Ventilation
What the domain covers
Sanitary Drainage, Sewerage, and Ventilation tests gravity drainage, soil and waste pipes, traps, vents, inspection chambers and connection to sewers or on-site systems.
Core rules
- Drainage relies on gravity and a continuous fall; the pipe must not run flat or backfall.
- Soil pipes carry human waste; waste pipes carry sinks, basins and baths; vent pipes admit air and protect trap seals.
- A trap holds a water seal. A P-trap is preferred to an S-trap because it is easier to vent and less likely to siphon.
- Ventilation relieves pressure in the stack and prevents gurgling, slow drainage and seal loss. A vent stack usually terminates above roof level with a cowl.
- Inspection chambers and manholes give access for cleaning; gully traps receive surface or fixture waste; septic tanks and soak pits serve where no public sewer exists.
Worked example
A 10 m house drain falls 200 mm from the building to the inspection chamber. The gradient is 200 mm ÷ 10 000 mm = 1:50, or 2%. Record it as 1:50 and compare it with the specified gradient for that pipe size. The reasoning is that gradient is fall divided by horizontal run, expressed as a ratio or percentage; a flatter drain risks solids settling, while an excessive fall can separate liquids from solids.
Traps that cost marks
Omitting venting and blaming the trap, using an S-trap where a P-trap is required, laying a drain with backfall, connecting rainwater to the sanitary sewer without approval, and forgetting access at changes of direction.