Rain may reveal a problem rather than cause it
Plumbing fixtures use water seals in traps to stop sewer gases entering the building. Vent pipes help the drainage system balance pressure. Heavy rain can raise water levels, saturate soil or load local drainage systems, making an existing fault more noticeable.
Possible causes to consider
- A dry trap: an unused floor waste, shower, sink or laundry drain may have lost its water seal.
- A faulty fixture seal: a damaged connection around a toilet or drain can let odour escape.
- A vent problem: a blocked, damaged or poorly performing vent can affect pressure in the drainage system.
- A partial blockage: slow drainage and trapped waste can create odours that become stronger under changing conditions.
- An outdoor overflow: a sewer or gully issue near an open window or air intake can carry odour indoors.
- Cross-connections or damaged pipework: a licensed plumber may need to inspect how the property drains are arranged.
Safe observations to make
Note the first room where the smell appears, which fixtures were used recently and whether any drain gurgles or runs slowly. Check rarely used fixtures and look for a visibly dry floor waste. If appropriate for the fixture, running a small amount of clean water can restore a dry trap, but it will not repair a broken seal, vent or pipe.
Outside, observe from a safe distance whether a gully, grate or inspection opening is overflowing. Do not remove drain covers, enter confined areas or lean over an opening to investigate.
Ventilate the area if it is safe, avoid flames and keep people away from any wastewater overflow. If anyone feels unwell, leave the area and seek appropriate medical or emergency advice.
How to tell a drain odour from a gas leak
Odours can be difficult to identify confidently. If you suspect natural gas or LPG, do not operate electrical switches or try to locate the leak yourself. Leave the area and contact the appropriate gas emergency service. Tell the plumber what the smell resembles, but do not rely on smell alone to declare it safe.
What to record for a plumber
- Which room and fixture seem closest to the odour.
- Whether it appears only during rain, after rain or at other times.
- Any gurgling, slow drainage or changes in toilet water level.
- Whether an outdoor gully or drain is overflowing.
- Recent renovations, long-unused rooms or known drainage work.
- The suburb and whether the property is a house, unit or commercial premises.
Drain help in Melbourne's south east
The South East Plumber connects enquiries with independent providers across Melbourne's south east and the Mornington Peninsula. Coverage, licensing, scope, timing and pricing are confirmed directly by the provider.
See the blocked-drain plumbing service, read what to do when a drain backs up, or describe when the smell appears.
Related plumbing services
Useful next steps: blocked drain plumbing, stormwater plumbing and drain cleaning.