Why does my drain smell like rotten eggs or sewage?
The smell is sewer gas, and it is reaching your nose because something has broken the barrier that normally keeps it in the pipes. Every fixture in your home has a water trap, the U-shaped bend under sinks and built into toilets and floor wastes. The water sitting in that bend is the seal between your bathroom and the sewer. When the seal is lost, evaporated, or bypassed, hydrogen sulphide and other sewer gases drift straight up the pipe. The smell itself is the symptom. The real question is which barrier failed, and that determines whether the fix costs nothing or needs a plumber.
What are the most common causes and fixes?
Here are the causes we find on the Gold Coast, roughly in order of how often we see them:
| Cause | Typical fix | Who fixes it | Cost as of 2026 |
|---|---|---|---|
| Dried-out floor waste or unused fixture trap | Pour a jug of water down it | You | Free |
| Biofilm and grease in basin, shower or sink waste | Clean the waste and trap | You | Free to cheap |
| Partial blockage letting waste sit in the line | Machine drain clear | Licensed plumber | $250 to $400 |
| Damaged or dislodged trap, failed seal at toilet base | Repair or reseal | Licensed plumber | $120 to $300 for most toilet repairs |
| Cracked drain or vent problem under or beside the house | CCTV inspection, then repair | Licensed plumber | $200 to $350 to diagnose |
How do I fix a smelly drain myself?
Start with water, then cleaning, and spend nothing until both have failed. First, pour a full jug of water down every floor waste and any fixture that rarely gets used, such as a guest ensuite shower or a laundry tub. Traps evaporate in two to four weeks of disuse in Queensland heat, and refilling them fixes a huge share of household drain smells overnight. Second, clean the biofilm: pull the pop-up waste out of the basin, clear the hair and grey slime, and scrub what you can reach. That slime is bacteria feeding on soap and skin, and it smells swampy even when the drain flows fine. A kettle of hot water with a little dishwashing liquid down the kitchen sink helps break down grease film. If the smell returns within days or was never touched by any of this, the cause is further down the line.
When does a smelly drain mean a blockage?
When the smell comes with slow drainage or gurgling, you are smelling a partial blockage. Waste that should flush away in seconds is instead sitting against a restriction, rotting in the pipe, and pushing gas back up through the water seals every time a fixture drains. This is the stage worth catching. A partial blockage cleared in normal hours is a $250 to $400 machine clear as of 2026. Left alone, it usually becomes a full blockage, and full blockages have a talent for arriving after hours, when the callout alone runs $360 to $560 for the first hour plus the work.
Why does the smell come from the grate in my yard?
A smell at the outdoor grated gully often means waste is sitting in your main sewer line, and that gully deserves attention because it is your overflow relief gully. It is deliberately set lower than your indoor fixtures so that if the sewer blocks, sewage surcharges into the garden instead of your bathroom. A persistent smell there, or worse, water pooling around it on a dry day, means the blockage is on your side of the connection and it is your responsibility as the owner to have it cleared. Do not seal or cover the grate to hide the smell. Blocking an ORG defeats a safety feature required under AS/NZS 3500 and turns the next surcharge into an indoor flood.
When should I call a plumber about a drain smell?
Call a plumber when the smell survives refilled traps and a proper clean, when it comes with gurgling or slow water, or when you can smell sewage outdoors. Those symptoms point at the buried pipework: a partial blockage, a broken vent, or a cracked drain leaking under the slab. We clear the line, and if the smell or blockage has happened before, we put a CCTV camera down it, $120 to $180 as an add-on while we are there, so you know whether this is a one-off or the first sign of roots or pipe damage. Persistent sewer smell with no visible cause is one problem you should not ignore, because the causes only get more expensive with time.
Smell that will not go away? Call Hills Plumbing & Gas on 0472 657 042. We find the cause, quote a fixed price before we start, and back it with QBCC licence 15243081 and 5.0 stars from 27 Google reviews. More on our blocked drains service.