Drainage and septic tanks
What did the visit record about failed haunching, about broken benching, and about flow the survey did not dye-test?
The visit recorded failed haunching and broken benching as things that could be seen in the chamber, and it recorded that the flow was not dye-tested. Haunching is the concrete around a pipe where it enters the chamber. Benching is the shaped concrete that should turn the flow through the invert. Those defects were visual. The survey did not put dye or water through the run, so it has not decided where the flow escapes, or whether the broken concrete is letting sewage out. The chamber was looked at. The pipes were not proved.
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?
When haunching falls away, the pipe can move at the chamber wall. When benching breaks, waste can sit in a rough channel or find a gap beside the invert. Both are real defects in what the surveyor could see once the cover was up. Neither one shows how the drain behaves further along the run. A dye test was not done, so arrival of the flow was not shown. The failed concrete is evidence of damage in the chamber. It is not a map of leakage underground.
Show the solicitor the chamber defects and make clear that flow was not tested. A drainage firm can dye-test the run and say whether the haunching and benching need rebuilding. The survey has not specified that repair and has not priced it. Do not fill the broken benching yourself before the flow is understood. A tidy new channel on a leaking pipe would hide the wrong problem. Keep the visible concrete and the untested flow as separate limits of the visit.
What should you ask your surveyor?
- Which pipes had lost their haunching, and which benching was broken?
- Was sewage standing in the chamber, or was the invert merely damaged?
- Could you see flow moving, even though you did not dye-test it?
What are the typical next steps?
- Record failed haunching and broken benching as seen, and the flow as untested.
- Ask a drainage firm to dye-test before repairs are specified.
- Tell the solicitor the underground run was not proved.
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 broken benching the same fault as a collapsed drain?
No. Benching is the concrete channel inside the chamber. A collapse would be the pipe itself, which this visit did not dye-test and may not have seen beyond the chamber wall. Failed haunching is the concrete around the incoming pipe. The survey recorded those chamber defects. It has not decided the buried run has collapsed.
Can the chamber be used while the benching is broken?
The survey has not decided that. Broken benching means the channel that should guide the flow is damaged, which can let waste sit or leak at the chamber. It does not, by itself, say the house cannot be drained tomorrow. A drainage firm needs to see the flow. Until that test, do not treat the chamber as either serviceable or finished.