A bad smell from a bathroom drain usually has a simple cause. Here is how to find and fix it.
A drain that smells of sewage or staleness is unpleasant but usually fixable. Here are the common causes and how to solve them.
A Dried-Out Trap
Every drain has a U-bend (trap) holding water that blocks sewer gases. In a rarely used shower or basin the water evaporates, letting smells in. The fix: run the water to refill the trap.
Blockages and Biofilm
Hair, soap and grease build a smelly biofilm in the pipe. Clean the trap and use a drain cleaner or a hot water and bicarbonate flush.
Failed Seals
A poorly sealed shower waste or toilet connection can leak odours. Re-sealing or refitting the waste solves it.
Venting Issues
If smells appear when other fixtures drain, the soil stack venting may be at fault — a job for a plumber to diagnose.
When to Call Us
If the smell persists after cleaning traps and wastes, there may be a drainage or venting fault worth investigating properly.
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Frequently Asked Questions
Why does my shower drain smell only sometimes?
Often a partially dried trap or biofilm. Running water refills the trap; a thorough clean removes the biofilm. Persistent smells may indicate a seal or venting issue.
Are chemical drain cleaners safe for bathroom pipes?
Used occasionally and as directed they're generally fine, but frequent use can damage seals. A bicarbonate-and-hot-water flush is gentler for regular maintenance.
