Track down smelly indoor drains, clean traps and gullies, refill dry traps, and deodorise safely without harsh chemicals.
SD-01Work out which drain is the culpritGo round each sink, bath, shower and floor gully in the house one at a time. Run the tap or shower briefly and sniff close to the plughole to see where the smell is strongest. A smell that's worse in a spare bathroom or utility room often points to a dry trap, while a smell near an outside gully points somewhere else entirely.
SD-02Refill any dry trapsEvery sink, bath and shower has a U-bend trap that holds a small amount of water to block sewer gas. If a drain is rarely used, that water can evaporate and let smells straight through. Pour a jug of water slowly down the plughole to refill it, then check again after 10 minutes. Do this every few weeks for spare bathrooms or unused showers.
SD-03Take apart and clean the trapPut a bucket underneath to catch water, then unscrew the trap under the sink or bath by hand or with pliers. Pull out hair, soap scum and grease, then rinse the trap under a tap. Check the rubber washers aren't split before screwing it back together hand-tight plus a quarter turn, then run the tap to check for drips.
SD-04Clear and deodorise the overflowThe overflow slot in a sink or bath gets slimy and can smell even when the trap is fine. Push a bottle brush or small drain brush through the overflow, then flush it through with hot water and a squirt of washing-up liquid. Repeat until the water runs clear.
SD-05Check the toilet sealLook and sniff around the base of the toilet where it meets the floor. A smell here, or staining on the floor, usually means the seal between the pan and the soil pipe has failed. Cleaning around it won't fix a failed seal — that's a separate job, so treat this step as a check, not a repair.
SD-06Clear outside gullies and drain coversKitchen and bathroom waste often runs out to an open gully outside. Clear away leaves, grease and debris with a small hand brush, then pour a bucket of water down it to flush it through and refill the water seal at the bottom. A gully that's dry or blocked is a common cause of smells travelling back indoors.
SD-07Check for a faulty air admittance valveSome sinks have a small dome-shaped valve under them instead of a vent pipe outside. Run the tap and hold your hand near the valve — if smell escapes there, it's failed and needs replacing. These push-fit onto the waste pipe and don't need any plumbing skill, just a firm push to remove and refit.
SD-08Deodorise the drainPour a handful of bicarbonate of soda down the drain, followed by a cup of white vinegar. Leave it fizzing for 15 minutes, then flush through with a kettle of hot (not boiling, for plastic pipes) water. Avoid bleach — it can damage rubber washers and seals and doesn't deal with the actual cause of the smell.
SD-09Tidy up and check it's workedBin any debris from the traps rather than putting it back down the drain, and wipe down tools before putting them away. Run all the taps and showers you've worked on again after an hour to make sure the smell hasn't come back. If it has, the smell is likely coming from further down the pipework, which is a job for a plumber.