The short answer
An overflow relief gully (ORG) is the outdoor drain grate that lets sewage escape outside if the sewer backs up, so it doesn’t come up through the floor wastes and toilets inside. If it’s full of water or overflowing, stop using water inside, keep people and pets away, and call a plumber: McDermott Plumbing on (08) 6187 3999 or text 0406 882 648. If wastewater is overflowing or causing damage, also call Water Corporation on 13 13 75 (24/7). A dry, smelly ORG is a different problem: its water seal has dried out.
What an ORG does
Building and Energy WA’s technical note on the plumbing standard (AS/NZS 3500.2) says a drainage system needs at least one overflow relief gully (there are only a few narrow exceptions), and the top of its riser has to sit at least 150 mm below the overflow level of the lowest fixture inside, or below the grate of an inside floor waste. That height difference is the whole point. If the sewer surcharges, sewage spills out of the lower gully outside before it can reach the shower base or toilet.
Where that 150 mm can’t be achieved, a reflux valve has to be fitted as well, but the technical note is clear that a reflux valve never replaces the ORG. On some sites the gully sits closer to the inspection shaft with a hose tap above it to keep its water seal topped up.
For the gully to work, the grate needs to sit loose and stay clear. Don’t screw it down, glue it, pave over it or bury it under mulch.
Why an ORG fills up or overflows
- A blockage in the property sewer further down from the gully: tree roots in an older line, wipes, fat, or a broken section. This is the usual cause.
- A blockage in Water Corporation’s main, which can back up into more than one property. If the neighbours are having the same trouble, mention it when you call.
- Rainwater getting in where garden beds, paving or lawn have built up around the gully, so stormwater runs into it instead of away from it.
- Leaves, sand or garden debris in the gully riser itself.
What to do right now
- Stop using water inside: no flushing, showers, dishwasher or washing machine until it’s sorted.
- Keep kids and pets away from the gully and any wet ground. Treat it as sewage and wash your hands after going near it.
- Don’t poke a hose or stick down it, and don’t tip in chemicals.
- Check whether the neighbours have the same problem.
- If wastewater is overflowing on the property or causing damage, call Water Corporation on 13 13 75. The line is attended 24/7.
- Call (08) 6187 3999 or text 0406 882 648 with your suburb, a photo of the gully, and which fixtures are slow.
A dry ORG that smells
If the gully smells but is dry, the water sitting in its trap has probably evaporated, which can happen over a hot Perth summer when nothing tops it up. Tipping a bucket of water in restores the seal. If the smell keeps coming back, or you can smell sewer inside as well, have it checked; a vent or trap problem may be the cause.
Who pays to clear it
Blockages in the property plumbing are the owner’s responsibility. Blockages in the sewer main, normally outside the property, are Water Corporation’s. If we find the problem is in the main, we report it, their crew clears it, and Water Corporation pays the plumber a standard fee for locating it. Our sewer responsibility page covers the landlord and tenant side.
What we do
We find where the blockage is, clear it from the right access point, and check that the gully drains down and holds a proper water seal again. We also look at the gully itself: whether garden beds or paving have built up around it, whether the grate has been fixed down, or whether it sits too high to protect the house, and tell you what we find.
Common questions
- What is an overflow relief gully?
- It’s the outdoor drain grate, usually near an outside wall, that lets sewage overflow outside if the sewer backs up, so it doesn’t come up through the toilets and floor wastes inside.
- Why is my ORG full of water?
- Usually because the sewer is blocked further down the line, on your property or in Water Corporation’s main. Stop using water inside and call a plumber. If it’s overflowing or causing damage, call 13 13 75 as well.
- Is an overflowing ORG an emergency?
- It’s urgent. The gully is protecting the inside of the house, but the blockage behind it won’t clear itself. Water Corporation says to call 13 13 75 immediately if wastewater is overflowing on your property or causing damage.
- Can I cover or pave over my ORG?
- No. It needs a loose grate, kept clear of soil, mulch and paving, and it must stay lower than the fixtures inside. Covering it defeats the purpose and can send sewage back into the house.
- Who pays to clear a blocked ORG?
- If the blockage is in your property plumbing, the owner pays. If it’s in Water Corporation’s main, they clear it and pay the plumber a standard locating fee.
Related pages
Official sources
Last updated 6 October 2026. General information only. Every property is different, so call us to talk about yours.