Drain smell in the bathroom or kitchen: causes and solutions

Quick answer. A drain smell almost always comes from a dry or dirty trap, debris built up in the drain, a worn seal or a downpipe that is not venting properly. Start by pouring water into drains you don't use and cleaning traps and grates. If the smell persists, or appears in several flats, the seals and downpipe need checking.

You walk into the bathroom and it smells of sewage, even though it has just been cleaned. You open the window, a while passes and it comes back. It is one of the most common queries and there is almost always a simple explanation. The key is to notice where it smells and when.

Quick diagnosis: where and when it smells

Where and when	Likely cause	Solution
In a little-used bathroom or after a holiday	Dry trap: the water has evaporated	Pour water into all the drains
At the kitchen sink	Grease and debris in the trap	Clean the trap under the sink
Around the toilet	Worn seal at the base	Check and replace the seal
When the neighbours use water, with gurgling	The downpipe is not venting and empties the traps	Check the downpipe and its ventilation
In several homes at once	Problem in the downpipe or sewer pipe	Tell the property manager

What you can fix yourself in five minutes

1. Pour in a bucket of water into showers, bidets and floor drains you don't use often. If the smell goes away, it was a dry trap.
2. Clean the grates in the shower and basin: hair and soap trap debris that ferments.
3. Take the trap off the kitchen sink with a bucket underneath and clean it. Grease is the biggest cause of bad smells in the kitchen.
4. Notice when it comes back: if it coincides with water being used in other flats, the problem is in the downpipe.

Plumber's tip: don't mask the smell with air fresheners or pour bleach down the drain every day. The smell is a warning: if you hide it, the problem is still there.

When to call a plumber

• The smell persists after filling and cleaning the traps.
• It comes with gurgling, water draining slowly or blockages.
• It smells around the toilet or there is damp at its base.
• It affects several homes in the building.

In these cases the source is usually in the seals, the pipework or the building's downpipe. If the water is also draining slowly, see our guide on the blocked downpipe.

Frequently asked questions

Is a drain smell dangerous?

It is mainly unpleasant, but it means gases from the sewer system are getting into the home. It is best to ventilate and deal with the cause.

Why does it smell worse when it is hot or at night?

In hot weather, the water in the traps evaporates faster. At night it is more noticeable because there is less ventilation. Pouring water into little-used drains is usually enough.