Drainage and septic tanks

A rainwater downpipe appears to enter a foul gulley. Has the survey proved a misconnection?

No. It has seen a downpipe whose shoe looks as if it discharges into a gulley that also smells or looks like a foul waste, which is a visual suspicion rather than a traced pipe or a camera survey. Approved Document H is about how drainage is designed for regulated work, and it does not prove where this pipe goes.

Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.

What is the fuller explanation?

Misconnections put rain into foul, or foul into rain. The survey can see the above-ground mistake when a downpipe clearly drops into a gulley that takes a basin or a washing machine, or when foul water stands in a rain channel. It cannot see the sewer the gulley joins once the pipe is below ground. One shoe in one gulley is one observation. It is not a map of the street. Do not tell the seller the survey has already convicted the house. Say which pipe and which gulley, and that the run was not traced.

A drainage firm can dye-test or camera if you need the route before exchange. That is an extra. Lifting one cover, if it was lifted, still does not follow a downpipe. RICS home surveys are visual. They do not award drain-camera grades, and this page will not invent any. If you ask for a quote, give the firm the photograph and the sentence, not a retelling that says “all the drains are cross-connected”. Rain into a small private system can also matter, but do not turn one gulley into a septic-tank calculation. The next step is to identify the pipe.

What should you ask your surveyor?

Which downpipe and which gulley did you see?
Did you trace the pipe underground, or only see the shoe?
Are you calling this suspected, not proved?

What are the typical next steps?

Do not dig the gulley out on a viewing.
If the route matters, ask a drainage firm to trace that pipe. Keep the instruction to what was seen.
Do not describe the whole street as misconnected because one shoe looks wrong.

Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.

Also asked about this

Is a downpipe that splashes onto the ground the same note?

No. That soaks the wall. A shoe in a foul gulley is a different observation. Do not merge them.

Does a bad smell prove the rainwater is in the foul sewer?

It supports a concern. It does not trace the pipe. The survey did not camera it.