A bad smell from a drain is one of the most common drainage complaints we receive. It’s unpleasant and can range from a mild musty odour to a strong sewage smell that fills a room. The good news: most drain smells have a straightforward cause, and many can be fixed without calling anyone.
Cause 1: Dry Trap (Most Common)
Every sink, bath, and shower has a U-shaped section of pipe called the trap. It holds a small amount of water that acts as a seal against sewage gases rising from the sewer into your home.
If a fixture isn’t used regularly — a guest bathroom, a utility room sink, a holiday home — the water in the trap evaporates. With no water seal, gases rise freely.
Fix: Run water into the fixture for 30 seconds. That’s it. For infrequently used drains, pour a small amount of cooking oil down after running water — it sits on top of the water and slows evaporation.
Cause 2: Partial Blockage and Decomposing Debris
A build-up of hair, grease, food waste, or soap scum creates a breeding ground for bacteria. The smell is the odour of organic material decomposing in warm, damp conditions.
Signs: The smell is worse after running water. Drainage may be slightly slow.
Fix: Clear the trap manually (it unscrews under the sink). For deeper blockages, try pouring boiling water down the drain, followed by a baking soda and vinegar solution. If this doesn’t work, professional drain jetting clears the pipe walls thoroughly.
Cause 3: Cracked or Damaged Pipe
A hairline crack in a drain pipe allows waste water and gases to escape into the surrounding soil and structure. In older Manchester properties with clay or pitch fibre pipes, this is more common than people expect.
Signs: The smell doesn’t improve after clearing blockages. It seems to come from the walls or floor rather than the drain opening itself. Damp patches may appear near drainage pipes.
Fix: A CCTV drain survey will locate the crack. Depending on its size and location, the solution is either pipe relining (no excavation needed) or excavation and replacement.
Cause 4: Blocked or Inadequate Vent Pipe
Your drainage system has vent pipes — usually running up through the roof — that allow air into the pipes and sewage gases to escape safely outside. If a vent pipe is blocked (leaves, bird nests, ice in winter), pressure builds in the system. This can cause gurgling sounds, slow drainage, and sewage odours inside.
Signs: Gurgling sounds from toilets or drains after use. Smells seem to come from multiple fixtures simultaneously.
Fix: Clearing a roof vent is a job for a professional — it involves roof access and working safely at height. Call us on 0161 282 8080 and we’ll assess whether the vent is the issue.
Cause 5: Issue in the Main Sewer or Shared Drain
If the smell is throughout the property rather than from a specific fixture, the source may be further down the system — in the main sewer line, in a shared drain, or even in United Utilities’ public sewer.
Signs: Smell affects whole property, not one room. Neighbours may have the same problem.
Fix: Check with neighbours. If the problem is shared, report to United Utilities (0345 672 3723) for the public sewer, or call us to survey the shared drain section.
DIY Maintenance to Prevent Drain Smells
- Run all infrequently used drains weekly to keep traps full
- Clean sink traps every three to six months — they unscrew by hand or with a wrench
- Avoid pouring cooking fat down any drain
- Don’t flush wipes, cotton buds, or sanitary products — they build up in pipes and rot
- Pour a kettle of boiling water down kitchen and bathroom drains monthly to dissolve grease and soap
When to Call a Professional
Call us if:
- The smell returns quickly after DIY cleaning
- You notice slow drainage alongside the smell
- The smell seems to come from walls or floors rather than drain openings
- You can’t identify the source
- There are damp patches near drainage pipes
A CCTV drain survey is the definitive way to find the cause when DIY methods don’t work. Call 0161 282 8080 or contact us online.
We cover Manchester, Salford, Stockport, and all of Greater Manchester.
Frequently Asked Questions
Is a drain smell dangerous?
Sewage gases (including hydrogen sulphide and methane) are harmful in high concentrations. At the levels typical in a domestic property, the risk is low, but persistent exposure is unpleasant and the underlying cause should be fixed. Ventilate the affected area and get the problem diagnosed.
My new shower tray smells — why?
New shower trays often have a dry trap straight out of the box. Run the shower for two minutes to fill the trap. If the smell persists, check that the trap is properly connected and seated.
I’ve poured bleach down the drain but the smell comes back within days. What next?
Bleach masks smell temporarily but doesn’t remove the debris causing it. You need either a thorough manual clean of the trap, professional jetting, or — if it keeps returning — a camera survey to rule out a structural issue.