TL;DR
Most blocked outside drains start with leaves, silt, grit or cooking fat sitting in the gully trap. A stiff brush or a set of drain rods clears many of them. Never force rods against firm resistance, and do not tip anything down a gully that you would not pour down a kitchen sink. If more than one gully backs up, or water comes up indoors as well, stop, because that points to shared pipework. Request a free quote online and describe what you see.
What an overflowing gully is telling you
The small grated gully outside the back door or under a downpipe is where wastewater and rainwater join the underground drain. If it drains slowly, or water sits above the grate after the rain stops, the blockage is usually in the trap below. It might be leaves, silt, moss, grit or fat that set hard after going down a nearby sink.
A gurgle from an indoor sink or toilet while the gully is slow is a useful clue. Air is being pushed back up the pipe as water tries to pass a restriction. Therefore, the blockage probably sits between the gully and the point where that branch joins the main run.
Clearing it safely, step by step
Lift the grate and clear anything in the trap by hand, wearing gloves. Many blockages end at this point, because open gullies collect a lot of leaf litter and grit. Coastal areas such as Saltdean area may see extra wind-blown debris.
If the trap is clear but water still will not drain, try a stiff drain brush or a short set of hand rods. Feed the rods in with a steady turning motion instead of pushing hard. You want to work through the blockage, not punch a hole in old pipework. If you feel firm resistance, stop, since it is more likely a displaced joint, a root or a collapse.
Avoid boiling water, caustic soda and shop-bought drain cleaners on an outside gully. Older clay or cast-iron pipes can suffer from sudden heat or strong chemicals. They also rarely clear anything beyond the first metre of pipe.
Why gullies block more than you would expect
Open gullies collect whatever the weather and the garden send their way. Leaves, grit and soap residue settle fastest in the trap, right where the pipe changes direction. Heavy rain can also wash fine silt into older drains, which slowly narrows pipes that were never generous in size.
Shared drainage adds a third factor. In many older buildings, several properties share one drain run. A blockage that looks like your gully may belong to next door as well, so clearing your own trap will not fix it. This can happen anywhere from Woodingdean area to Patcham area. Our guide to blocked drain causes explains the pattern in more detail.
When to stop and get it looked at
Stop clearing it yourself in any of these cases.
- More than one gully or fixture is affected at the same time
- The blockage comes back within days of clearing it
- You smell sewage rather than stagnant water
- Your rods meet solid resistance that you cannot work past
Any of these points beyond a single trap. It could be a blocked drain further down the run, a damaged pipe, or the boundary where the water company takes over. Southern Water can tell you who is responsible for your section. A CCTV drain survey shows what is happening underground, and our article on what a survey shows explains how. Pricing depends on the drain, so read about what affects survey cost first.
If the outside blockage has caused a toilet to back up indoors, treat that as more urgent. Read how to unblock a toilet for what to do and avoid. A slow shower alongside the gully may be covered by our advice on unblocking a shower drain.
FAQs
Can I use chemical drain cleaner on an outside gully? We would avoid it. Cleaners are made for indoor waste pipes, and on older pipework they can damage seals and joints without clearing the blockage.
How do I know if it is my drain or a shared one? If a neighbour's gully backs up at the same time as yours, it is likely shared. A CCTV survey can trace where the run belongs to you and where it joins a shared pipe or public sewer.
Is it safe to keep rodding if I meet resistance? No. Firm resistance usually means something structural, and forcing it can turn a clearable blockage into a repair.
If your outside drain keeps blocking, request a free quote online. We cover gully problems for homes in Lancing area and nearby areas too.
