The Gully Trap Is Overflowing: What That Actually Means

Wastewater coming up out of a grate beside your house looks like a disaster. It is unpleasant and it needs dealing with quickly, but the first thing worth knowing is that the gully trap is doing exactly what it was designed to do.

It is the relief point. When your drain blocks, the wastewater has to surface somewhere, and the gully is there so it surfaces outside on the ground rather than inside through your shower and floor wastes. If you are looking at a mess in the garden, the alternative was the same mess in the bathroom.

What is a gully trap?

A round grate at ground level, usually against an outside wall, sitting over a trap that holds a water seal. Your kitchen, laundry and sometimes basin wastes discharge into it, and the water seal stops drain smells coming back up.

Two things follow from that. It is deliberately the lowest opening in your drainage system, which is why it surcharges first. And its rim is meant to sit above ground level and below the floor level inside, so that overflow goes out rather than in.

An outdoor gully trap grate beside a house

What do I do right now?

Stop using water. Every flush, shower and wash cycle adds to what is coming out. This matters more than anything else you can do.
Keep children and pets away from it. Treat it as a health issue, not just a mess.
Do not hose it into a stormwater drain. That puts wastewater into the stream network. Contain it if you can, and let us wash it down properly.
Do not tip drain cleaner down it. It will not clear a blocked main, and it makes the line unpleasant for whoever has to work on it.
Note what was running when it started. Whether it surfaces only when the washing machine drains, or whenever anyone flushes, genuinely narrows down where the blockage is.

Is it my drain or Watercare’s?

This is the question worth asking early, because the answer can change who pays for the whole job.

Your private drain runs from the house to the point where it joins the public sewer. That connection is the boundary. A blockage inside your property is yours. A blockage at or past the connection is Watercare’s.

We took an after hours callout on a Saturday in Birkdale where a gully trap at the front of the property was actively overflowing, with toilet paper discharging from it, and the upstairs shower had been draining slowly since the tenants moved in. We cut an inspection point into the toilet stack, hydro jetted the line and cleared it, but clearing it alone did not resolve the fault. So we ran a camera down.

The CCTV showed the line was blocked near the council connection, which we verified against Watercare’s GIS records. That put the fault on the council side, not in the private drainage.

A CCTV still from a drain survey, with the distance along the line shown

The part most people do not know: you may be able to claim the cost back

Because that blockage was at the council connection, the cost of the work could be claimed back from Watercare by the property owner.

We notified Watercare, they issued a Service Request number, and that number went on the invoice so the owner could lodge the claim. Once the invoice is paid we provide a paid copy of the drainage contractor invoice to support it.

This only works if somebody establishes where the blockage actually was, which in practice means a camera. If a drain is cleared and nobody looks, there is no evidence and no claim. It is one of the better arguments for a CCTV inspection on a job like this.

Why did it block?

Three causes account for most of what we see.

Tree roots. The most common on older clay and earthenware lines. At a property in Northcote the tenants reported water and sludge spilling out of the gully at the rear. We jetted the line clear, then put the camera down and found two separate sections of tree root intrusion in the rear lawn, at 1.2 and 1.5 metres deep and about 1.5 metres apart, on a fall of around minus 15 degrees.

Food waste. In Hobsonville a kitchen waste and gully were blocked with a large amount of egg shells and fruit peel from the waste disposal. Shells and fibrous peel do not break down, they pack. The disposal is not a rubbish bin.

Wipes, fat and the rest. Anything that does not break down finds the first rough joint and starts collecting.

Food waste cleared from a blocked kitchen waste line

Clearing it is not always fixing it

This is the part worth being blunt about, because it decides whether you are back here in six months.

After that Northcote job we told the owner plainly: the line is clear and draining normally now, but the blockage was caused by roots entering through two failed pipe joints, and those joints will keep drawing roots back in. Clearing it is a temporary fix, not a permanent one. The permanent fix is repairing the joints, and we quoted that separately.

A jetter clears what is in the pipe. It does not repair what let it in. If a drain has blocked more than once, the useful question is not “can you clear it” but “what is in there that keeps catching things”, and the camera is how you answer that.

Gully overflowing now? Call us. Say whether it is running continuously or only when water is used inside, because that tells us how fast we need to be.

Common questions

Why does mine overflow when it rains, with no blockage?

Then something is putting stormwater into the wastewater line, which it should not be. A downpipe connected into the gully, or a gully with its rim set too low so surface water runs in, will surcharge the sewer during heavy rain. It is worth sorting, because the same fault contributes to overflows across the network and it is your pipework doing it.

Is the smell from the gully dangerous?

The smell itself is unpleasant rather than dangerous, but it is telling you the water seal in the trap has been lost, either through evaporation in a dry spell or because the trap has been disturbed. Pouring a bucket of water down it restores the seal. If the smell comes back within a day or two, something else is going on and it is worth a look.

Can I clear it myself with a hose or a rod?

You may shift a shallow blockage close to the gully, and it is a reasonable thing to try if the overflow is mild. What you cannot do is reach a root intrusion 1.5 metres down in the back lawn, and pushing a rod hard into old earthenware can break it. If water is still surcharging after a gentle attempt, stop and call somebody with a jetter.

How much of this is the tenant’s responsibility?

Stopping water use and reporting it promptly is the tenant’s part, and doing that fast genuinely limits the mess. The repair is the owner’s. Where a blockage is clearly caused by what has gone down the drain, such as a disposal packed with shells, that can become a conversation between owner and tenant, which is a good reason for our report to say exactly what we found in the line.

Do I really need the camera, or can you just clear it?

If it is a first blockage and the cause is obvious, clearing it is often enough. Put the camera down when it has blocked before, when clearing does not fully resolve it, or when you want to know whether the fault is on the council side, because that last one can pay for the whole job. It also gives you something concrete to quote a repair from rather than a guess.