Foul Drain Smell — What to Do Right Now
A sewage smell in the house is almost always a dry trap, a failed seal, or a broken soil-vent pipe. Not usually an emergency — but it does need finding, because the fumes can be harmful with prolonged exposure.
Make it safe — before anything else
Ventilate the room
Sewer gases (methane, hydrogen sulphide) are low-concentration in a domestic leak but shouldn't be breathed in for hours on end. Open windows.
Never light a naked flame if the smell is strong
Very rare, but a strong methane build-up is flammable. Ventilate first, don't strike a match.
Don't mask with chemicals
Bleach + drain deodoriser can react with waste and produce chlorine gas. Fix the cause, don't mask.
Keep pets away
Dogs and cats are more sensitive to sulphur gases. Move their beds out of any room with the smell.
What Kevin (our AI) will check first
Message Kevin and he'll ask exactly these questions before we send an engineer, so we bring the right parts on the first van.
- Where exactly is the smell — one room, or throughout the house?
- Constant, or worse at certain times (after rain, when the boiler fires, when neighbours flush)?
- Any unused toilets, sinks, shower trays or floor drains in the property?
- Age of the plumbing — pre-2000 plastic waste, old lead traps, or modern push-fit?
- Is there a soil vent pipe visible above roof level, or an internal air-admittance valve (AAV) under the sink or in the loft?
Common causes of a foul drain smell
Dry trap on an unused fixture
Every waste has a U-bend that holds water — a seal against sewer gas. In unused sinks, showers and floor drains the water evaporates. Refill by running for 30 seconds.
Failed toilet pan seal
The wax or rubber ring between the WC and the soil pipe perishes. Smell around the base of the pan; often a small water mark on the floor too.
Failed air-admittance valve (AAV / Durgo valve)
AAVs let air into the soil stack but seal against outflow. When they fail, sewer gas vents into the loft or under-sink cupboard. Replacement is quick and cheap.
Broken or badly-routed soil vent pipe
Cracked internal soil pipe, or an external one venting too close to a window. Needs a survey to confirm; often a repair sleeve or re-route.
Sludge in a rarely-used waste run
Fat, hair and biofilm build up in low-flow waste pipes and start producing sulphur gas. High-pressure clean fixes it.
Honest cost band — why we won't quote blind
Typical
£120 – £260 for a diagnosis visit, trap refill and simple AAV or pan-seal replacement
Complex
Soil-vent-pipe repair or reroute £320 – £950. CCTV survey if the smell is unresolved £180 – £320.
A dry trap costs nothing to fix; a broken soil pipe in a wall is a proper job. £50 diagnostic gets you a written fixed price for the real cause.
Fixed £50 diagnostic
Flat fee. No hourly meter running.
Fair quote or refund
Transparent pricing — refunded if we don't fix it.
Vetted UK engineers
DBS-checked, insured, real reviews.
AI-triaged in seconds
KJ chats first so the right engineer arrives.
Related emergencies
See all in the emergency plumbing hub — or the leaks & water damage hub.
Areas we cover for foul drain smell
Same-day across Greater Manchester and Rochdale.
Foul drain smell — FAQs
Dealing with a foul drain smell? Chat with Kevin now
Real triage in seconds. £50 diagnostic visit — refunded if we don't fix it.
Related hubs: emergency plumbing, leaks & water damage, all services.
Chat with Kevin about Foul drain smell