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Most drainage faults a plumber is called to come down to a lost trap seal, a blockage or a poor fall. The free question set checks how traps lose their seals, how stacks and branches are vented, what Approved Document H expects of seal depths, branch lengths and falls, and how to trace a smell or a slow drain to its cause.
A seal can be pulled out by the appliance's own discharge, pulled out by another appliance discharging nearby, pushed out by pressure at the foot of a stack, or lost slowly to evaporation or to a thread of debris over the weir. Each has its own symptom and its own cure.
Revise the ways a seal is lostA discharge stack is vented so the air pressure inside it stays close to the air outside as water falls through it. An open vent at the top or an air admittance valve lets air in; blocking either lets a discharge pull on every trap connected below.
Revise single-stack drainageA gradient of 1 in 40 means 1 mm of fall for every 40 mm of run, so divide the run length by 40 for the fall. Too little fall lets solids settle; too much lets the water run away from them.
Work through a fall calculationFor a drainage question, follow the water from the appliance through its trap and branch to the stack and the drain, and note where air gets in. For a smell or a gurgle, ask which seal is being lost and what is pulling or pushing it. For a fall, turn the gradient into millimetres over the length of the run before comparing answers.
A drainage mock test checks recall without the explanation after each answer, so you see which ideas hold up on their own. Drainage is one unit of Level 2 plumbing theory; test the other units in your course as well.
The free test offers 5, 10 or 25 questions from this same set, with an optional practice timer. In Test mode, answers and explanations appear after you finish. Repeated tests reuse this bank, so a higher score can reflect familiarity.
Set up a free Drainage and sanitation testIn England, Approved Document H covers drainage and waste disposal, including trap seal depths, branch pipe sizes and lengths, stack ventilation and the falls of below-ground drains. Check the edition your course uses, and the equivalent guidance if you work in Wales, Scotland or Northern Ireland.
Divide the length of the run by the gradient number: 5 metres at 1 in 40 is 5,000 mm divided by 40, which is 125 mm. Keep the length in millimetres so the answer comes out in millimetres too.
Yes. The Test setup uses 5, 10 or all 25 questions from this set. Choose an optional practice timer and review the explanations after finishing. For broader plumbing revision, add the cold water, hot water and plumbing science sets as well.
All 25 questions on this page are free, with no account or card required. They are selected from the maintained Drainage and sanitation question bank. Premium opens the full bank of 125 questions, more modules and Weak-Spot Review.
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