Drainage and septic tanks
What is a misconnection, and will a home survey trace one?
A misconnection is a foul pipe, often from a sink, washing machine or toilet, that discharges to a surface-water drain or a ditch instead of the foul sewer. A surveyor may see a washing-machine hose into a rainwater gulley. They will not dye-test the whole house unless that was agreed. Seeing one hose is not a map of every pipe.
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 pollute watercourses and they are a drainage defect, not a roof defect. Approved Document H describes how drainage should be arranged for work under the building regulations. It does not certify an existing Victorian terrace. The survey records what is visible: a hopper taking a bath waste, a gulley that smells, a pipe with no trap.
The water company or a drainage contractor can trace the rest. Do not assume the whole street is wrong because one hose is in the wrong gulley. Ask the surveyor which pipe they saw. Correcting that pipe may be a small job or may open a floor. There is no RICS national price. Get a quote after the pipe is identified.
What should you ask your surveyor?
- Which appliance or pipe did you see going to a surface gulley?
- Did you test with dye, or only look?
- Is the recommendation to alter that pipe, or to survey all the drains?
What are the typical next steps?
- Do not redirect a pipe into another gulley yourself during a viewing.
- If a toilet is involved, treat it as urgent to investigate. A sink hose is still worth correcting, but it is not the same.
- Ask a drainage firm to trace before you agree a figure with the seller.
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 rainwater pipe into a foul gulley the same mistake?
It is the other way around, and it can overload the foul sewer. The survey should say which way the wrong connection runs.
Does a septic tank house have this issue?
It can. Surface water should not be sent into a small treatment system. GOV.UK’s septic-tank pages are about foul drainage. Keep rainwater out of that system.