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.

A dirty gully does not automatically mean the underground pipe is damaged

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 repeatedly fills again soon after being cleaned, the next step is to look farther along the run rather than keep treating the same surface symptom.

When to consider a camera survey

A camera is most useful after the drain has been opened and cleaned. It can then show whether roots, open joints, fractures or heavy deposits are creating a place for solids to catch. A camera pushed through dirty standing water may tell you little.

Useful checks you can make from ground level

Notice what happens when different fittings discharge. If running the kitchen tap makes the outside gully rise almost immediately, the kitchen branch is reaching the gully and the restriction is farther on. If only rainwater causes the overflow, foul drainage may be completely separate and the problem may instead involve a surface-water line or soakaway.

Also look at the chamber covers you can reach safely. A chamber that is already full before any water is used tells a different story from one that fills only when a particular appliance empties. Do not climb into a chamber or try to work from inside it.