Outside Drain Overflowing

First work out whether the water is coming up or failing to get away

If water poured into the gully simply sits there, the restriction may be close by. If the level rises when a toilet is flushed or a washing machine discharges, the obstruction is likely to be on the common run that those fittings use.

Where an inspection chamber is accessible, comparing the water level in one chamber with the next chamber downstream can narrow the location considerably. A full chamber followed by an empty one points to the section between them.

Clear the gully trap before blaming the buried drain

Leaves, silt and grease can obstruct the gully itself. In older gullies the trap can also hold a surprising amount of debris. Clearing the visible pot may therefore restore flow without any work to the buried drain.

If the gully pot is clean but the water soon rises again, open the next accessible chamber. Its level will tell you whether the restriction is between the gully and that chamber or farther downstream.

When to consider a camera survey

After the blockage is opened, clean the run before judging the pipe. A camera cannot assess a joint hidden under grease or muddy water, but a clear view can show roots, a step at a joint or a fracture exactly where waste keeps catching.

Checks that can narrow down the blockage

Run one fitting at a time and watch the gully. If the kitchen tap makes it rise, that branch is reaching the gully and the blockage lies farther along. If the gully overflows only in heavy rain, check the surface-water drainage or soakaway rather than assuming a foul-drain blockage.

Look from ground level into any chamber you can open safely. A chamber already full before anyone uses water shows a downstream blockage. One that rises only when a particular fitting empties helps identify which branch is feeding the problem. Never climb into a chamber.