Why every sanitary appliance has a trap and why stacks are ventilated.
Every sanitary appliance has a trap holding a water seal that stops foul air and drain gases entering the building. Common appliance trap seals are around 75 mm deep.
Soil and waste stacks are ventilated so that pressure changes as water discharges do not siphon or blow out the trap seals. Approved Document H sets the scope for foul, waste and rainwater drainage.
*Original revision guidance; verify seal depths against current standards.*
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