Blockages, Drains and Sewers
Above-Ground Sanitation and Drainage · Plumbing
A blocked sink and a blocked sewer need very different responses. This topic shows how to tell them apart, how to clear the simple ones safely and who is responsible for the rest.
How many outlets are affected points to where the blockage sits: one slow basin suggests its own trap, the whole house suggests the stack foot or drain, and neighbours as well suggests a shared sewer. Fat, wipes, hair and food waste cause most household blockages.
A plunger with the overflow covered, and a trap cleaned out over a bucket, deal with most local blockages. Chemical cleaners need care: never mix two of them, and never plunge after pouring one in.
In England and Wales a property owner looks after the drain inside the boundary, while most lateral drains and shared sewers passed to the sewerage companies in 2011. Escaping sewage, a solid obstruction or sinking ground above a drain are signs to stop and bring in a drainage contractor or the company.
Count the affected outlets first
Updated
How to reason about the system
One slow outlet points to its own trap or branch, every outlet in the house points to the stack foot or the drain, and neighbours affected as well points to a shared sewer. Clear what is local and hand the rest on.
Questions to take further
- Who is responsible for a blocked drain outside my house?
- In England and Wales the owner looks after the drain serving only their property inside the boundary, and since October 2011 the sewerage company has looked after most lateral drains and shared sewers. Scotland and Northern Ireland have their own arrangements.
Sources
- GOV.UK: Approved Document H — Guidance for England on above-ground drainage, traps, venting, access and rainwater disposal; guidance is not itself the legislation.
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Lessons on the plumbing path
- Finding where a blockage is
- Clearing a trap or waste safely
- Drains, sewers and who owns them
- Inspection chambers and when to stop
Terms to know
Before you start: some plumbing work is regulated or notifiable
Some water fittings work needs notice to, and consent from, the water supplier before it starts. Check the rules where you live.
Gas work is for competent workers covered by a Gas Safe registered business in Great Britain. Northern Ireland has separate gas regulations. Do not work on gas pipes or appliances yourself.
In England, installing an unvented hot-water system over 15 litres is notifiable building work: use a competent installer registered with a competent-person scheme, or tell building control before work starts. Leave this work to a suitably skilled person.
Wales, Scotland and Northern Ireland have their own water and building rules; check which apply before work starts. Electrical connections belong with an electrician.
This guide does not qualify you or make you competent, approved or registered for plumbing, gas or unvented work.