Drain smell in the bathroom or kitchen: where it comes from

It's almost always a trap. Start with water.

The answer in 2 lines. A drain smell nearly always comes from a trap, the bend under a sink, bath or shower that holds a little water to block sewer air. A shower nobody uses dries out, a trap full of hair starts to smell, a worn toilet seal lets air through. Run water, clean the trap, and if the smell keeps coming back, think about ventilation of the waste pipes. But if it could be gas, treat it as gas: get out and call 0800 111 999.

The first 3 steps

Run water for a minute in every little-used outlet: guest shower, basin, floor drain, utility sink.
Sniff outlet by outlet, plug out, to find the worst one.
Open the windows wide while you look.

Stop: danger

Smell of gas: gas smells of rotten eggs, like a drain. If in doubt, treat it as gas: no switches, no flames, open windows, turn off the gas at the meter if you can reach it easily, get out and call the National Gas Emergency Service on 0800 111 999 from outside. Free, 24/7, in England, Scotland and Wales.
Never mix drain unblocker, bleach or descaler: some mixtures give off toxic gas.
Sewage coming up through a drain, toilet or manhole: don't use water, keep children and pets away, and call your water company (shared sewer) or a drainage engineer.

Where is the smell coming from?

A shower, basin or floor drain hardly used: the trap has dried out, the water has evaporated. Run water regularly.
A basin or shower that drains slowly: a dirty trap (hair, soap). Take it apart and clean it.
Around the base of the toilet: the seal between the pan and the soil pipe is worn. Have the pan connector replaced.
A gurgle when the bath empties, and the next trap empties too: the waste pipes aren't vented properly. An air admittance valve or venting needs checking.
Near the washing machine: the waste hose isn't connected to a trap, or isn't pushed in properly. Connect it to a trapped standpipe or sink waste.
Around the whole building or outside, especially in warm weather: a shared drain or the sewer. Tell the building manager, or your water company.

Cleaning a trap, step by step

Put a bowl under the trap (the U-bend or bottle trap under the basin or sink).
Unscrew the nuts by hand, without tools if you can, and empty the trap into the bowl.
Pull out hair and gunk, rinse in hot water with a brush.
Check the rubber washers: a squashed or split one is replaced with the same size.
Screw it back by hand, run the water and check for drips.

What not to do

Pouring in a drain unblocker, then taking the trap apart: risk of burns.
Covering the smell with air freshener: the cause is still there.

If the smell comes back

Shower trap: the grille lifts out; the hair catcher and the inner part clean like a basin trap.
Basin overflow (the small hole near the top of the basin): it gets dirty too; flush it with hot water.
Venting: waste pipes need to "breathe" through a vent pipe or an air admittance valve, or the traps get sucked dry. That is a plumber's job: WaterSafe lists approved plumbers by postcode: WaterSafe — Finding a plumber.
Going away for a while: before you go, pour a little water into each trap; when you get back, run water everywhere.

Good to know

The small amount of water held in the trap is called the water seal: it is what stops sewer air coming back up.
A smell in the street or from a manhole is for your water company to deal with, not you.

Who pays and who to call

If you rent: in England, the landlord must keep drains, sinks, basins, baths and toilets in repair (Landlord and Tenant Act 1985, section 11). Report a smell that keeps coming back, or a worn toilet seal, in writing. Clearing a trap you blocked with hair is usually down to you.
Shared drains and sewers: since 1 October 2011, in England and Wales, sewers shared with neighbours, and the part of your own drain outside your property boundary, belong to your water and sewerage company, which deals with blockages and smells from its network at no cost to you.
In a block of flats: shared soil stacks and their vents are the freeholder's or managing agent's responsibility.

In your city: your sewerage company

London: Thames Water.
Birmingham: Severn Trent.
Manchester and Liverpool: United Utilities.
Leeds and Sheffield: Yorkshire Water.
Newcastle: Northumbrian Water.
Bristol: Wessex Water for sewerage (your tap water comes from Bristol Water).
These are the companies for most of each city. Your water bill shows which company handles your sewerage.

In Norwich, Hannah smells drains in the guest bathroom, unused since the summer. She runs the shower and the basin for a minute each. The next day the smell has gone: the traps had dried out.

A made-up story, for illustration.

Bobby

Sources, verification, confidence

Verified on 1 November 2026, for England. Confidence: high for the causes and the trap steps; high for the gas emergency number and advice (gas networks); high for the 2011 sewer transfer and section 11; medium for who pays in a rented home, which depends on the cause. We found no official statistics on drain smells in homes, so we don't quote one. This guide describes common cases, not a diagnosis.