An outside drain or gully smelling bad is easy to dismiss, especially if it comes and goes. But a persistent smell from an external drain usually has a specific cause, and in most cases it’s worth working out what it is rather than living with it.
Start with the gully trap
Most external drains have a gully trap, a U-shaped section designed to hold a small amount of water that acts as a seal against smells travelling back up from the sewer. If this trap has dried out, been damaged, or was never fitted correctly, sewer gas can escape straight up through the gully and into the air around it.
Common causes of an outside drain smell
- A dry or damaged gully trap, losing its water seal against sewer gas
- Debris trapped in the grate, such as leaves or food waste, rotting where it sits
- A partial blockage further down the line, causing waste to sit and decompose instead of flowing away
- A cracked or displaced section of external pipework, letting waste escape below ground near the gully
What you can check yourself
It’s fine to clear visible debris out of the grate and give the gully a rinse with a bucket of water, which can top up a dry trap and settle the odour temporarily. If the smell comes straight back, that’s a sign the cause is further down than a quick clean can reach.
When it needs a proper look
A smell that persists after cleaning the gully, or that’s accompanied by slow drainage, gurgling, or damp patches nearby, usually means there’s a blockage or a fault in the pipework itself. Our engineers can trace the exact cause with a CCTV drain survey, rather than repeatedly rinsing a gully that’s masking a bigger problem.
If your outside drain still smells after a clean, call us on 0333 200 1623 and we’ll help you find out what’s causing it.