Most drain smells come from a dried-out trap in a little-used shower or floor waste, which lets sewer gas into the room. Run water for 30 seconds to refill it. If the smell stays, the cause may be a blocked vent, a failed toilet seal, a partly blocked drain or a broken pipe, which a plumber can find.
What a trap does
Every sink, basin, shower, bath, floor waste and toilet has a trap: a bend in the pipe that holds a small amount of water. That water forms a seal that stops sewer gas coming up the pipe and into the room, while still letting waste water flow away.
If the water in the trap evaporates or gets sucked out, the seal is broken and sewer gas comes straight up the drain. That’s the classic rotten-egg or sewage smell.
Causes and fixes
| Where the smell is | Likely cause | Fix |
|---|---|---|
| Spare bathroom, laundry floor waste, unused shower | Dry trap from lack of use | Run water for 30 seconds; repeat every week or two |
| Shower or basin | Hair, soap and skin build-up in the waste | Remove the grate and clean it out |
| Kitchen sink | Fat, food scraps and soap in the trap and pipe | Hot water and detergent; clear the blockage |
| Around the base of the toilet | Failed seal between the pan and the sewer pipe | Plumber |
| Several drains, with gurgling | Blocked or damaged vent pipe | Plumber |
| Throughout the house or yard | Partly blocked, cracked or broken drain | Plumber, often with a CCTV inspection |
Easy fixes to try first
- Run water in every drain for 30 seconds, including floor wastes (pour a bucket of water in) and the spare shower.
- Clean the shower and basin wastes. Lift the grate and pull out hair and gunk with gloved fingers or a drain claw.
- Flush the kitchen sink with hot water and a squeeze of detergent to shift grease.
- Check the toilet for movement or water around the base.
- Skip chemical cleaners. They mask the smell briefly and can damage seals and pipes. Our guide on how to unblock a drain covers safer methods.
If the smell goes after refilling the trap and comes back a week later in a room you rarely use, it’s almost certainly just evaporation. Run the water regularly.
Need a local plumber?
Morrisons Maintenance Plumbing has served Caloundra to Maroochydore for 14+ years. Book a plumber or call 1300 149 288.
When a smell means a bigger problem
Call a plumber if:
- the smell is strong, lasts after you’ve refilled the traps, or is spreading through the house
- drains are gurgling or slow as well as smelly
- there are damp patches on walls or floors near the smell
- you can smell sewage in the yard, or there’s sewage around the overflow relief gully
- the trap refills but smells again within a day
These point to a vent that isn’t working, a failed seal, or a drain that’s partly blocked, cracked or broken. Vent pipes let air into the drainage system so water flows smoothly; when one is blocked, draining water can suck traps dry. A broken pipe under the house or slab can let sewer gas into the building.
A plumber can check the traps, test the vents and run a CCTV camera through the drain to find the cause. For roots and cracked pipes, see our guide on tree roots in drains.
Coastal homes and holiday rentals
Holiday homes and units that sit empty for weeks are prone to drain smells, because every trap in the house slowly dries out. Owners and property managers can:
- run all taps, showers and floor wastes at each clean or inspection
- ask guests or cleaners to run water in the spare bathroom
- have a plumber check vents and seals if smells keep returning even with regular use
Sewer gas is unpleasant and in higher concentrations can be harmful, so don’t ignore a strong or lasting smell. See our blocked drains service or book a plumber.
Frequently asked questions
Why does my bathroom smell like sewage?
The most common reason is a dry trap in a shower, basin or floor waste that isn’t used often. Without water in the trap, sewer gas comes up the drain. Run the tap for 30 seconds. If the smell persists, a vent, seal or pipe may be at fault.
How do I stop my drains from smelling?
Run water in little-used drains every week or two, clean hair and soap from shower and basin wastes, and keep fats out of the kitchen sink. If the smell keeps coming back, have a plumber check the traps, vents and pipes.
Can a blocked vent cause drain smells?
Yes. Drain vents let air into the system so water flows smoothly. If a vent is blocked, draining water can suck traps dry, letting sewer smell in. Gurgling drains are a common clue.
Is sewer smell in the house dangerous?
Sewer gas is unpleasant and in higher concentrations can be harmful, so don’t ignore a strong or lasting smell. Air the room, refill traps, and get a plumber to find the cause if it doesn’t clear.
Why does my kitchen sink smell?
Kitchen sink smells usually come from fats, food scraps and soap building up in the waste and trap. Flushing with hot water and detergent helps. If it’s slow to drain or smells constantly, the pipe may need clearing.
Honest, upfront pricing from a local, family-owned plumber.
Call 1300 149 288 or request a quote. QBCC licence 1296541.