Drain odours almost always come from a dried-out or faulty odour seal, or from debris decomposing in the trap. Keeping the water seal intact, cleaning the trap regularly, and checking the outlet connection normally resolves it.
Main causes
| Cause | Explanation | Fix |
|---|---|---|
| Dried-out water seal | Water in the trap evaporates in bathrooms used rarely | Run water regularly, or use a trap with a larger water volume |
| Debris decomposing | Hair, soap and biofilm accumulate in the channel or trap | Clean the grate and trap thoroughly |
| Shallow trap | Low-profile drains have less water seal depth | Fit a drain with a dry trap or cartridge seal if the water seal is insufficient |
| Pressure fluctuation | Air movement in the pipe pulls the seal | Check the venting and the trap type |
| Poor outlet connection | Leak or open joint downstream | Inspect and reseal the connection |
| Dry trap drain | Some low-depth drains use mechanical or membrane seals | Check the seal is seated and undamaged |
Practical prevention
- Flush every shower drain weekly, including in guest or spare bathrooms.
- Clean the hair trap before it overflows into the channel.
- Avoid pouring grease, oils or food waste into shower drains.
- In hotels and buildings with seasonal occupancy, include drain flushing in the room-opening checklist.
- Check the odour trap type suits the installation — very shallow floors may need a different seal design.
If the smell persists
- Clean the trap and channel completely — including the channel walls, not just the trap.
- Run hot water through for several minutes.
- If the odour returns quickly, inspect the outlet for leaks or open joints.
- Confirm the trap is the correct type for the installation depth.
Related: cleaning a linear drain