Where does my sewage go? And what about stormwater?

Flush the toilet or pull the plug and it's gone, but where to? Homes in Sydney have two separate drainage systems: the sewer, which takes wastewater away for treatment, and the stormwater system, which carries rain off your roof and yard. They go to very different places, and mixing them up causes real problems. This guide follows both from your house to the ocean, with a local twist: for most of the southern Eastern Suburbs, the sewage ends up just down the road at Malabar. It's written by the licensed plumbers and drainers who work on both systems every week.

Step 1: from your fixtures to your sewer pipe

Every toilet, shower, bath, basin, sink, dishwasher and washing machine drains into pipes under the floor or slab. Each fixture has a water trap, the U-shaped bend under a basin or built into a toilet, which holds a little water to keep sewer gas out of the house. The pipes join together and run out through the yard as your private sewer line.

Outside, you'll usually find an overflow relief gully: a small grate near the house, set lower than your floors. If the sewer ever blocks, sewage spills out of that grate in the yard instead of coming up through your shower or toilet. It's worth keeping it clear and never covering it with pavers or garden beds.

Step 2: into Sydney Water's sewer

Your private line connects to a Sydney Water sewer main, either under the street or, on many older blocks in Matraville, Maroubra and Botany, through the back or side yard. From there, sewage flows mostly by gravity through bigger and bigger pipes, with pumping stations lifting it where the ground doesn't slope the right way. Our sewer responsibility guide explains which pipes are yours and which are Sydney Water's.

Step 3: the treatment plant at Malabar

For most homes in the southern Eastern Suburbs, the journey ends at the Malabar wastewater treatment plant, on the coast at Malabar. It's one of Sydney's largest, handling around a third of the city's wastewater from a catchment that stretches all the way to Sydney's south-west.

• Screening: rags, wipes, plastics and other solids are screened out first. This is where wet wipes and fats cause trouble for the whole system.
• Grit removal: sand and grit settle out.
• Settling: in large tanks, solids sink to the bottom and fats float to the top, and both are removed.
• Biosolids: the settled solids are treated and much of it is reused, for example on farmland.
• The ocean outfall: the treated water is piped out under the seabed and released more than two kilometres offshore, in water up to about 80 metres deep, where it disperses.

Homes further north, around the city and Paddington, drain to a similar plant at Bondi.

Where stormwater goes

Stormwater is completely separate. Rain from your roof runs through gutters and downpipes, and water from paths and lawns goes into pits and drains. On most properties it flows to the street kerb, into council's stormwater pits and pipes, and then straight out to the nearest creek, Botany Bay or the ocean. Stormwater is not treated. Whatever goes into it, from leaves to detergent, ends up at the beach.

See our stormwater guide and stormwater rules guide for how stormwater should be set up on your property.

Why keeping them separate matters

What this means in local homes

Older homes in Matraville, Maroubra, Malabar and Botany sometimes have downpipes that were connected into the sewer decades ago, or an overflow relief gully that's been paved over. Both are worth fixing. If your yard gully overflows in heavy rain, or your drains gurgle during storms, it's a sign stormwater may be getting into the sewer. A camera inspection shows exactly where your pipes run and how they're connected.

Related help: sewer responsibility guide, blocked drains, CCTV drain inspection, stormwater and our stormwater guide. Local pages: Malabar, Matraville, Maroubra and Botany. Browse all our plumbing guides.