Sewage backs up into a house when wastewater cannot flow away because the private sewer drain is blocked or damaged, or the public sewer is blocked or surcharged. Stop using all toilets, taps and water-using appliances immediately, keep everyone away from the sewage and arrange an urgent assessment by an appropriately licensed plumber. Once the source is controlled, follow safe sewage clean-up and exposure guidance.
What causes a sewage backup?
Common causes include:
- grease, wipes or other unsuitable materials blocking the drain
- tree roots entering a sewer pipe through cracks or defective joints
- cracked, displaced, sagging or collapsed drainage pipes
- a blockage or wet-weather surcharge in Sydney Water’s wastewater network.
A single blocked toilet, basin or shower usually indicates a local fixture or branch-drain problem. Several affected fixtures, wastewater rising when another fixture is used, or sewage appearing at the lowest drain suggests a blockage farther downstream or a public-sewer problem.
An overflow relief gully is designed to discharge wastewater outside before it rises through fixtures inside. An overflowing gully is therefore an important warning of a downstream restriction. Do not cap, cover or obstruct it, as this may redirect sewage into the house.
What should you do immediately?
- Stop adding wastewater: Do not flush toilets or use taps, showers, washing machines or dishwashers. If it is safe and accessible, close the property’s main water valve. This limits household discharge but will not stop flow from a surcharged public sewer.
- Avoid contact: Keep children and pets away, and do not touch or walk through sewage because it may contain harmful microorganisms.
- Stay clear of electrical hazards: If wastewater is near wiring, power points or appliances, do not enter the area or cross sewage to reach the switchboard. Contact emergency services if there is immediate danger; otherwise arrange safe isolation through the electricity distributor or a licensed electrician.
- Arrange urgent help: Contact an appropriately licensed plumber to identify whether the fault is in the private drain or Sydney Water’s network. If neighbours, the street or public wastewater assets are also affected, report the fault to Sydney Water and stay clear of the area.
Do not use chemical drain cleaners, remove sewer access covers, rod the drain or attempt to plug the overflow relief gully.
How is the underlying cause stopped?
The remedy depends on the blockage location and the pipe’s condition. A plumber can assess the affected fixtures and accessible drainage points, then use a sewer camera where needed to locate roots, damage or recurring obstructions.
A removable blockage may be cleared mechanically or with professional high-pressure water jetting. Repeated clearing will not provide a lasting fix if roots are entering through defects or the pipe is cracked, displaced or collapsed; the damaged section may need repair, relining or replacement.
Responsibility depends on the location of the fault. The property owner is generally responsible for private wastewater plumbing, while Sydney Water manages faults in its wastewater network. A plumber may first need to locate the problem before responsibility can be confirmed.
Where public-sewer surcharge repeatedly threatens a property, a licensed plumber can explain how sewer backflow devices work and assess whether a compliant reflux valve is suitable. It may restrict reverse flow in specified circumstances, but it will not clear a blocked private drain and requires professional selection and installation.
If sewage is actively backing up, keep clear and contact our licensed sewage plumbers for an urgent assessment.