Smelly Drains: Common Causes and How to Fix Them

A bad smell from a drain is unpleasant, and it is often a sign that something isn’t right. The good news is that many causes are simple to fix. This guide covers the usual suspects, from dry traps to broken pipes, and when to get the drains checked.

Start with the simple causes

Some smells come from inside the house, and you can often fix them yourself.

• A dry trap. Each sink, bath and shower has a U-bend that holds water. That water stops sewer gas coming back up. If a basin or shower goes unused for weeks, the water can dry out. Run the tap for a minute to refill it.
• Grease and food in the kitchen drain. Fat sets inside the pipe and traps food waste, which then rots. Since hot water alone rarely shifts it, a build-up may need clearing.
• Hair and soap in bathroom drains. These collect in the trap and start to smell. Clean the trap and the plughole.
• A loose or failed seal. A worn seal around a toilet or under a sink can let gas escape.

When the smell comes from outside

A smell around a gully, a manhole or the garden usually points further down the system.

• A blocked gully or run. Waste sits in the pipe and rots. A drain unblocking visit can clear it.
• A cracked or broken pipe. Sewage can leak into the ground, so the smell lingers even when nothing seems blocked.
• A shared drain problem. In older terraces, one blockage can affect several homes. Who is responsible for a blocked drain explains who should deal with it.

Shared runs are common in some housing, for example tenement closes in Glasgow and older shared drains in Manchester, as well as back-to-back terraces in Leeds. Who pays differs between Scotland and the rest of Great Britain, which the guide above explains. The list of cities covered links the rest.

Smells that come and go

A smell that appears after heavy rain, or when someone flushes, can point to a blockage further down. Water backs up, then drains slowly, and the smell comes with it. Still, it can also mean a vent pipe is blocked, which stops the system breathing.

When to get the drains checked

If cleaning the traps doesn’t help, or the smell keeps coming back, a camera check is the next step. A drain inspection is a short check aimed at one problem like this. It can show whether the pipe is blocked, cracked or letting roots in.

Ask the engineer to talk you through the footage. You then know whether you need a simple clear or a repair.

Smells and pests

Drains that smell often draw pests too. Small flies around a plughole may be drain flies, which breed in the slime inside pipes. Rats in drains are another sign, since rats can get in through broken pipes.

The bottom line

Start with the easy fixes: refill unused traps and clean out grease and hair. If the smell stays, or comes from outside, get the drains checked on camera rather than guess.

Send us your postcode and we’ll pass your request on straight away. Describe the smell and where it is, and ask for a written quote before any work starts.