Prevent sewer backflow by avoiding drain blockages, keeping the overflow relief gully clear and asking a licensed plumber whether a reflux valve suits your drainage system. Air gaps and water-supply backflow preventers protect drinking water; they do not stop sewage rising through toilets, showers or floor wastes.
Which devices help?
| Device | Purpose | Stops sewer backflow? |
|---|---|---|
| Reflux or backwater valve | Allows wastewater out, then closes against reverse flow | Can reduce reverse sewage flow, but cannot prevent every backup |
| Overflow relief gully | Provides an outdoor overflow point if the sanitary drain surcharges | No, but it can reduce the risk of wastewater overflowing indoors |
| Air gap | Physically separates a drinking-water outlet from a contamination source | No |
| Water-supply backflow preventer | Restricts contaminated water flowing back into potable-water pipework | No |
A reflux valve must suit the property’s pipe layout and remain accessible for inspection and maintenance. It cannot clear a blocked sewer drain or protect fixtures connected on the sewer side of the valve. A separate diagnosis is needed to identify what is causing a sewage backup. Selection, installation and sanitary drainage work should be left to a licensed plumber operating under AS/NZS 3500.2 (the national plumbing and drainage standard for sanitary plumbing and drainage, which sets mandatory pipe grades, venting rules, and fixture connections to prevent hazardous wastewater from surcharging back into living areas).
An overflow relief gully is not a valve. Keep its grate and surrounding area clear of soil, leaves, paving and stored items. Do not seal it, cover it or alter its height.
Reduce the risk of a backup
- Flush only toilet paper and human waste. Put wipes, nappies and sanitary products in the bin, even if labelled “flushable”.
- Keep fats, oils and food scraps out of sinks.
- Act on recurring slow drains, gurgling or blockages; these can indicate a restriction but do not confirm its location.
- Maintain any reflux valve according to its manufacturer’s instructions.
- Have recurring problems or a high drain-backflow risk assessed by a licensed drainage plumber.
These measures reduce preventable blockages but cannot stop every surcharge in the wider sewer system.
If wastewater is backing up
Stop using toilets, taps, showers, washing machines and dishwashers. Keep people and pets away from the affected area, avoid contact with wastewater, and do not use chemical drain cleaners or keep flushing to test the drain.
Do not open sewer pits, lift access covers or enter confined spaces. Sewage, gases and sudden wastewater movement are hazardous. If wastewater is near electrical fittings or appliances, do not enter the area or touch electrical equipment.
Water rising in a shower when a toilet is flushed can indicate a downstream sanitary-drain restriction, but it is not conclusive. For an active sewage backup or recurring drain surcharge, contact Fixed Today—Sydney's trusted drainage specialists for over 15 years. When you call, our dispatch team asks whether wastewater is overflowing inside or outside, if you live in a single-level home or multi-storey terrace, and whether your property has earthenware or PVC pipes, ensuring our emergency response vehicle arrives equipped with CCTV drain cameras and high-pressure water jetters ready to clear and inspect the blockage.