Sewage Smell in the Bathroom? Causes and Fixes
By Emergency Plumb,
A sewage smell in a bathroom means air from the drain is getting into the room. Plumbing is designed so that never happens, so the smell points to one of a few specific failures, and most can be found in a few minutes.
Short answer: Run water into every plughole, including any shower or bath that is rarely used, and flush the toilet. If the smell goes, a trap had dried out. If not, check the toilet base for a failed seal, look for a slow or gurgling drain, and check that the waste pipes are properly joined under the bath and basin.
How traps keep the smell out
Each fitting has a trap: a bend in the waste pipe that holds a small plug of water. Waste flows through it, but the water stays behind and blocks air from the drain. Almost every bathroom sewage smell is that water seal failing in one of four ways.
1. A trap has dried out
A guest bathroom, a shower nobody uses, or a floor drain in a wet room can sit for weeks until the water in the trap evaporates. Run each tap or shower for a few seconds and the smell should clear within the hour. If a trap keeps drying, use the fitting weekly or ask about a trap with a dry seal valve.
2. A trap is being siphoned empty
When a large volume of water rushes down a shared pipe, such as a bath emptying or a toilet flushing upstairs, it can pull the water out of a nearby trap. You might hear a basin gurgle as it happens. The cause is usually a waste run that is too long or too shallow, or a blocked or missing vent. That needs the pipework altering, and an air admittance valve is often part of the fix.
3. The toilet seal or connector has failed
Look and sniff at the base of the toilet. A pan connector joins the toilet outlet to the soil pipe, and when its rubber perishes or the pan moves, sewer air escapes around it. A damp floor, a stain behind the pan or a smell that is strongest after flushing all point here. See our guide to a leaking toilet pan connector.
4. A loose or broken waste joint
Under a bath or basin, a push-fit or compression joint that has come apart lets drain air into the void, and the smell then creeps out through gaps around the bath panel. Take the panel off and look for damp, staining or a pipe that pulls free.
When it is the drain, not the bathroom
If several fittings drain slowly or gurgle, or the smell is also outside near a manhole, the problem is further down the drain: a partial blockage or a damaged pipe. Our guide to bad smells from your drains covers the drain side, and our CCTV drain survey finds damage you cannot see.
Questions people ask
Why does my bathroom smell like sewage but nothing is blocked?
Most often a trap has lost its water. Every basin, bath, shower and toilet has a U-bend of water that blocks the smell from the drain; if it dries out, siphons empty or leaks, the smell comes straight through even though the water drains normally.
Why does my toilet smell like sewage?
Check the base first. A perished seal or loose pan connector where the toilet joins the soil pipe lets sewer air out around the pan, and sometimes a little dirty water each flush. A cracked pan or a seal under a close-coupled cistern can do the same.
Why does the smell come and go?
An intermittent smell often means a trap is being siphoned, for example when a bath empties or a toilet upstairs flushes, pulling water out of another trap. It can also follow the weather, when wind across the roof vent pushes air back down the soil pipe.
Is a sewage smell dangerous?
The smell is unpleasant rather than an emergency in most homes, but it means drain air is getting in, so find the cause rather than masking it. If sewage is visibly backing up into a bath, shower or toilet, stop using the water and treat it as a blocked drain.