Bad smell from toilet or floor drain
A nasty sewage smell around your toilet is one of the most unpleasant household problems you can face, but the good news is it's usually fixable without calling an engineer. The culprit is almost always one of three straightforward issues: the water seal in your toilet trap has dried out, the silicone seal at the base has failed, or the rubber connection behind the pan has perished. This problem affects homes of all ages, though it's particularly common in guest toilets or bathrooms that don't get regular use. The smell occurs because sewer gases escape into your living space when these seals fail — it's not just unpleasant, it indicates a genuine drainage issue that needs attention. This guide walks you through the most common causes and practical fixes you can tackle yourself, though if the smell persists after these checks, you'll want a drainage specialist with CCTV equipment to investigate further.
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Most likely cause & what to check
A sewage smell from around the toilet most commonly comes from one of three sources: a dry trap, a failed pan-to-soil-pipe seal, or a cracked soil pipe.
Check the toilet trap — if the toilet is rarely used, the water seal in the trap can evaporate, allowing sewer gas to enter the room. Flush the toilet and pour a litre of water into the pan to re-establish the seal.
Check the silicone seal at the base of the toilet where it meets the floor — if this has failed, sewer gas and waste can seep out. Remove the old silicone and reseal with sanitary-grade silicone.
If the smell persists despite these checks, the soil pipe connection at the back of the toilet may have a failed rubber doughnut seal. This requires pulling the toilet forward slightly to access and replace the seal.
A persistent smell with no visible cause may indicate a cracked soil pipe behind the wall — a drainage engineer with a CCTV camera can diagnose this.
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Frequently asked questions
Why does my toilet smell like sewage even though it looks clean?
The smell is coming from sewer gases escaping through failed seals or a dried-out trap, not from visible waste. A dry toilet trap is the most common cause — if the toilet isn't used regularly, the water seal evaporates, creating a direct route for gases to enter your home. A quick flush and pour of water often solves this immediately.
Is a smelly toilet dangerous or just unpleasant?
Whilst the smell itself is unpleasant, sewer gases can pose health risks with prolonged exposure, so it's worth addressing promptly. More importantly, the smell indicates a breach in your drainage system's integrity — whether that's a failed seal or cracked pipe — which could lead to waste contamination or water damage if left unchecked. It's not an emergency, but it shouldn't be ignored.
How much does it cost to fix a smelly toilet?
If it's a dry trap, it costs nothing — just a flush and water pour. Resealing the base with silicone costs roughly £20–50 in materials if you do it yourself, or £150–300 if you call a plumber. A failed rubber pan connector or cracked soil pipe will be more expensive; a drainage engineer's CCTV survey typically costs £200–400, with repairs ranging from £300 to £2,000+ depending on severity.
Can I fix a cracked soil pipe myself?
Not safely — soil pipes carry raw sewage and require proper disconnection, removal, and replacement work that demands building regulations compliance and professional certification. Attempting this yourself risks environmental contamination, structural damage, and invalidity of your home insurance. Call a qualified drainage engineer or plumber if CCTV confirms a cracked pipe.
Why does my guest toilet smell more than others?
Guest toilets are used infrequently, so the water seal in the trap evaporates faster than in regularly-used bathrooms, allowing sewer gas through. The trap is designed to hold water as a barrier — if no one's flushing regularly, that barrier disappears. Running water down the toilet weekly or keeping the lid down can help, but a flush with a water pour is the quickest fix.
Will opening windows or using air freshener solve the problem?
They'll mask the smell temporarily, but they won't fix the underlying issue — the faulty seal or dry trap will still allow sewer gases through. You need to address the root cause: rehydrate the trap, reseal the base, or replace the pan connector. Temporary solutions will fail, and you'll be back where you started.