The overflow relief gully, explained
Updated October 2026
Almost every sewered house in the Redlands has one, almost nobody knows what it is for, and it is the single most useful thing in the yard when a drain goes wrong. The overflow relief gully is the grated drain outside, usually near a bathroom or laundry wall, set deliberately lower than the lowest fixture inside the house.
Its job is to fail first. If the sewer line blocks and pressure builds, the water finds the lowest opening in the system and lifts that grate. The waste goes onto the ground outside instead of up through your shower, your floor waste or your toilet. That is not a fault. That is the gully working exactly as designed, and it is the reason a blocked sewer is usually an outdoor mess rather than an indoor one.
What it tells you, and when
The gully is a diagnostic as much as a safety valve.
- Overflowing while nobody is using water. This is the one that matters. Redland City Council's own test says that if the gully overflows when no water is being used on the property, the blockage is likely to be in its sewer main. Clear any obstruction, check the grate moves freely, then contact the council.
- Overflowing only when the washing machine empties or the bath drains. A partial blockage downstream that cannot take a surge. Still a blockage, usually still yours, and worth a camera before it becomes a full one.
- Smelling but not overflowing. Often a dry trap, especially on a gully that rarely sees water. Sometimes the first sign of a slow line.
- Full of leaves, mulch or soil. Common in the leafy old streets around Ormiston, Wellington Point and Birkdale, where figs, eucalypts and melaleucas drop constantly. A gully that cannot lift cannot protect the house.
The three things worth doing now
Nobody does maintenance on a drain they have never thought about, so keep it to three.
- Find it. Walk the outside wall near the bathroom and laundry and look for a round grate at ground level, often in a concrete surround. On older Redlands properties it is regularly buried under a garden bed, a pot or a deck.
- Keep it clear and keep it liftable. Rake the leaves off it, keep mulch and soil off the surround, and do not stack anything on top. The council's advice is to check the grate still moves freely.
- Do not raise it, cap it or pave over it. A gully that has been built up level with a new patio, or sealed, has lost its whole purpose. If landscaping has covered yours, get a licensed plumber to sort the level properly rather than leaving the house as the next lowest opening.
Why this matters more on flat bayside ground
The Redlands mainland is low-lying coastal land with flat grades, and old stormwater and sewer runs on the foreshore streets at Thorneside, Wellington Point, Cleveland, Victoria Point and Redland Bay have very little fall to work with. Less fall means solids settle instead of flushing through, and it means a surge takes longer to clear.
Tides add to it. When a king tide coincides with heavy summer rain, surface water has nowhere to drain and the whole system backs up at once. The gully is the designed release point in that situation, which is exactly when people are most tempted to block it to stop the mess. The stormwater, tides and surcharge page goes into what can actually be done about ground that floods.
What it is not
The overflow relief gully is not a floor waste, not a stormwater pit and not somewhere to tip anything. It connects to the sewer, so a bucket of pool backwash, paint water or washdown goes into the wastewater system. Stormwater pits and sewer gullies are separate systems in the Redlands and mixing them causes problems in both directions.
It is also not a substitute for finding out why the line blocked. A gully that has overflowed twice is telling you something about the pipe, and in the old bayside suburbs that something is usually roots at a clay joint. A CCTV inspection is the next step, and jet blasting cleans the pipe wall rather than punching a hole through the blockage.
Unsewered properties do not have one
On Russell, Macleay, Lamb and Karragarra islands, at Amity Point, across much of Dunwich and Point Lookout, and on the rural blocks at Mount Cotton, Sheldon and acreage Redland Bay, there is no sewer main and no council connection point, so an overflow relief gully in the sense described here does not apply. On those properties the equivalent early warning is wet or smelly ground over the tank or the disposal area, and the whole system is the owner's. The septic and on-site wastewater page covers what to watch for.
Frequently asked questions
Is the overflow relief gully mine or the council's?
The gully and the drainage on your side of the connection point are yours. The council's main is the council's. The inspection opening is also the owner's to install and maintain, which the council states plainly.
Sewage is coming out of the gully. Should I block it?
No. It is spilling outside so it does not spill inside. Keep people and pets away from it, stop using water in the house, and get a licensed plumber onto the blockage.
Can I put a cover over it to stop the smell?
A removable grate cover that still lifts under pressure is different from capping it. If there is a persistent smell, the trap is probably dry or the line is slow, and that is worth diagnosing rather than covering.
My new patio covered the gully. Does that matter?
Yes. The gully has to remain the lowest opening in the system and it has to be able to lift. If a renovation has buried or raised it, have a licensed plumber correct it before you find out the hard way.