Overflow relief gully: what it is and why it overflows
Updated 28 Oct 2026
Water or sewage at the grate near your house? That is the gully doing its job. Here is what it means and who fixes it.
An overflow relief gully is a grate in the yard, usually near the house. It lets sewage spill outside instead of inside when the sewer line is blocked. If it overflows, a pipe is blocked. Stay clear and call a licensed plumber.
Is it a plumber job?
Quick checks you can do from a safe distance.
Look, don't touch
- Is water or sewage coming out of the grate or the ground around it?
- Is it still happening when no rain has fallen?
- Are the toilet or shower gurgling or draining slowly as well?
- Stop using water in the house while you find out.
Don't do this
- Don't walk through or play in the wet area. Sydney Water says to stay clear of wastewater overflows.
- Don't try to clear the pipe yourself. A licensed plumber clears private-side blockages.
Sewage overflowing means a blocked pipe somewhere. Get a licensed plumber to look.
What is an overflow relief gully?
It is part of your home's sewer drain. You can usually spot it as a grate or cap on a short pipe in the yard. It is usually near the house wall.
Sydney Water describes these gullies as something that should operate like a safety valve. The NSW Government says the riser top must be at least 150 mm above the lowest fixture in the house. It also says at least 75 mm above the finished ground.
Why does my house have one?
If the sewer line blocks, wastewater has to go somewhere. The gully is built to be the lowest point on purpose. So the overflow comes out in the yard, not up through a floor drain inside.
So an overflowing gully is a warning. The gully is working, and something downstream is blocked.
What does it mean when it overflows?
The sewer pipe is blocked or full. The blockage may be on your side or in the street. Heavy rain can also push extra water into the sewer, which is why stormwater should never be connected to it.
| What you see | What it can mean |
|---|---|
| Only the gully overflows, in dry weather | A blockage in the pipe after it, such as roots or something flushed. |
| Gully overflows and other drains gurgle | The main line is likely blocked. Treat it as an emergency. |
| Only overflows in heavy rain | Stormwater may be getting into the sewer. A plumber should check. |
Whose pipe is it, mine or Sydney Water's?
It depends where the blockage is.
| Where | Who is responsible |
|---|---|
| Pipes on your property, up to where they join the network | You. Sydney Water says a licensed plumber must clear a blockage in private pipes. |
| The wastewater network pipes | Sydney Water. Call its faults line on 13 20 90, which Sydney Water lists as open 24 hours. |
Not sure which side it is? Sydney Water has system connection diagrams. In a unit block, ask your strata manager first. For a blocked sewer in the street network, report it to Sydney Water.
What are the common faults with an overflow relief gully?
Each one can send sewage the wrong way. A plumber can check them all.
| Fault | Why it matters |
|---|---|
| Grate sits too low | Sydney Water says gullies too close to the ground let surface water in. |
| Paving or a garden bed covers it | The overflow has nowhere to escape. NSW says a gully in a path must be finished to prevent ponding and water getting in. |
| Grate or cap is missing | Rain, soil and leaves fall straight into the sewer pipe. |
| Rainwater gets in | Stormwater pipes and drains should not feed the gully. Sydney Water checks this on inspections. |
Why use a licensed plumber?
A licensed plumber has the camera and jetting gear to find the real cause, not just the symptom.
- Ask for the plumber's NSW licence number.
- For any repair or raising of the gully, ask for a compliance certificate.
- If sewage reached your home, ask your insurer if they need a plumber's report on the cause.
Does this happen on the Northern Beaches?
Heavy rain is a reason to check the gully. See these local pages:
- blocked drains in Narrabeen, where gurgling points to the sewer
- emergency help in Narrabeen, for sewage in a floor drain
- blocked drains in Collaroy, near storm debris and roots
- blocked drains in Belrose, where tree roots reach old joints
What changes the price
Ask for a quote before work starts. These are the things that move it.
| Factor | Why it matters |
|---|---|
| Where the blockage is | A short run near the gully is quicker than a long main line. |
| Cause | Roots or a broken pipe may need a repair, not just clearing. |
| Gully changes | Raising or moving the gully is extra work, and may involve paving. |
Overflow relief gully questions
Why is there water coming out of the grate near my house?
The sewer pipe is probably blocked, and the gully is letting it spill outside. Stay clear of the wet area and call a licensed plumber.
Why does my house smell like sewage?
A sewer smell inside can come from a blocked drain or a dry or faulty trap. A plumber can find out which.
Why is my drain gurgling?
Gurgling can mean air is being pushed past a partial blockage. If several drains gurgle, the main line may be blocked, so call a plumber.
Can I cover the gully with paving or garden?
No. A covered gully cannot let the overflow out. Ask a licensed plumber to check the level before you build over it.
Who do I call for a blocked sewer?
Call a licensed plumber for your own pipes. Call Sydney Water on 13 20 90 if the fault is in the network.
Water at the grate and not sure why? Tell us what you're seeing and a licensed plumber can take a look.
Get a plumber to check it
A licensed plumber calls you to book a time that suits.