A smelly drain or gully: where is it coming from?

A sewer smell in the house is a different problem from a blockage — and often easier to fix. The pattern tells you a lot: does the smell come from one gully or drain, is it worse after a weekend away or in warm weather, or does it hang through the whole house? One smelly gully almost always points at that gully itself; a sewer smell that lingers everywhere or keeps returning points deeper.

The most common cause is a dry trap. Every drain point has a water seal: a bend holding water that keeps sewer air out. If that water evaporates — in a guest bathroom, a basement gully or during a holiday — the sewer is in open connection with the room. The second suspect is a dirty trap or a clogged-up gully: hair, soap residue and grease form a layer that starts to smell on its own.

Two special cases. The outdoor gully also has a water seal, and a gully silting up with leaves and sand starts smelling especially in summer. And sometimes the culprit is the sewer vent: if it is blocked, a flushing toilet sucks the traps elsewhere in the house empty — you hear glugging and then smell sewer air.

What you do yourself takes five minutes. Pour a generous jug of water into every drain point that sees little use — that refills the water seal and instantly fixes a dry trap. Unscrew the trap under the sink or basin (bucket underneath), clean it and put it back. Empty the shower drain. Baking soda with vinegar then helps against the smelly film in the pipe, though it won't shift a real clog. Finally, check the washing machine and dishwasher connections: a drain hose sitting too deep or too loose in the standpipe lets sewer air escape along the rim — connecting it properly per the manufacturer's diagram fixes this surprisingly often.

Call a technician if the smell returns within days while the traps are clean and filled, if the odour hangs in several rooms or in the crawl space, or if drains are also gurgling or running slow — the latter points at a sewer blockage in the making. If the source stays untraceable, the cause can sit in the pipe itself: a loose joint or a crack letting sewer air into the crawl space. A camera inspection (€ 85-175) then shows exactly where the pipe leaks or has come loose, so there is never unnecessary breaking or digging. The full rates are in the price index.