The short answer
Most shower and bathroom sewer smells come from a dry trap: the water sitting in the P-trap or floor-waste gully has evaporated, so sewer gas can rise into the room. Pour a jug of water slowly into the floor waste and run the shower and basin for half a minute. If the smell clears and stays gone, keep topping the unused drains up. If it returns within a day or two, or you also hear gurgling or see slow drainage, call McDermott Plumbing on (08) 6187 3999 or text 0406 882 648. Don’t tip caustic drain cleaners in — they won’t fix a dry seal or a failed pan seal, and they make the job harder.
Why a trap stops sewer gas
Every shower, basin, bath and floor waste that connects to the sewer needs a water seal. In practice that is the bend of water in a P-trap, or the water held in a floor-waste gully. Building and Energy WA’s technical notes on AS/NZS 3500.2 talk about being able to inspect and maintain that water seal at gullies and inaccessible fixture traps — the seal is what keeps sewer air out of the room.
When the water evaporates, the seal is gone. That is common in a second bathroom that nobody uses, a floor waste that only ever sees splash from the shower, or a house left empty over summer. The same idea shows up outdoors: a dry overflow relief gully smells for the same reason.
What to try before you call
- Pour a litre or so of water slowly into the bathroom floor waste, then run the shower and basin for about 30 seconds so every trap in the room refills.
- If the bathroom is rarely used, tip a teaspoon of mineral oil on top of the water in the floor waste after you refill it. The oil film slows evaporation; it is a temporary top-up, not a repair.
- Check the outdoor overflow relief gully too. If that grate is dry and smelly, tip a bucket of water in. Our overflow relief gully page covers the case where the gully is full rather than dry.
- Sniff near the base of the toilet. A smell that is strongest at the pan, especially after the floor waste has been topped up, can mean the toilet’s waste seal (the ring under the pan) has failed.
- If the smell clears and stays cleared, make a habit of running water in unused bathrooms once a fortnight in summer.
- If the smell comes back quickly, several rooms smell at once, drains gurgle when you flush, or an outdoor gully is filling up, stop guessing and call (08) 6187 3999 or text 0406 882 648.
When it isn’t just a dry trap
- Failed toilet waste seal: the ring under the pan has dried, cracked or shifted, so gas escapes at the floor. Rocking the pan gently, or a smell that is strongest at the base after traps are full, are clues.
- Blocked or restricted sewer vent: air can’t enter the system properly, traps get pulled dry when fixtures drain, and you may hear gurgling. Vents finish above the roof; birds’ nests and debris are a common cause.
- Partial blockage further down the property drain: gas is pushed back through the nearest open path. Slow showers, a gurgling toilet and a wet overflow relief gully point this way — see our blocked toilet and sewer blockage pages.
- Build-up in the shower waste itself: hair and soap scum smell musty rather than like raw sewer. Cleaning the grate and trap helps, but if the odour is clearly sewer gas, treat it as a seal or drain problem first.
What we do
We find which trap or seal has failed, refill or renew what needs it, and check whether a vent or a deeper drain problem is emptying the seals again. You’ll get a straight answer on the cause. If the smell is coming from a blockage that is backing sewage toward the house, we clear it from the right access point and tell you what we found.
If wastewater is overflowing on the property or causing damage, also call Water Corporation on 13 13 75. A smell alone is usually a plumbing job; an overflow is urgent for both of us.
Common questions
- Why does my shower smell like sewer in the morning?
- Often the floor waste or a rarely used trap has dried overnight, especially in hot weather. Pour water into the floor waste and run the shower. If the smell returns every day, the trap may be getting pulled dry by a vent or drain problem.
- Will pouring bleach or drain cleaner fix a smelly shower?
- No. Chemicals don’t restore a water seal, won’t reseal a toilet pan, and can damage fittings. Refill the traps with water first. If that doesn’t last, call a licensed plumber.
- Can a dry floor waste make the whole bathroom smell?
- Yes. The floor waste is often the weakest seal in a spare bathroom because it sees the least water. Once it dries, sewer gas comes straight up through the grate.
- When should I call a plumber for a bathroom sewer smell?
- If topping up the traps doesn’t clear it, if it returns within a day or two, if more than one room smells, if drains gurgle or run slow, or if you can smell sewer at the base of the toilet. Call (08) 6187 3999 or text 0406 882 648.
- Is a sewer smell dangerous?
- Treat it seriously. Sewer gas is unpleasant and can indicate a failed seal or a drainage fault. Ventilate the room, refill traps, and get it checked if it persists. If sewage is overflowing, keep people and pets away and call 13 13 75 as well as a plumber.
Related pages
Official sources
Last updated 9 October 2026. General information only. Every property is different, so call us to talk about yours.