Drainage and septic tanks

This flat’s WC gurgles when another flat flushes. Can the survey prove the stack?

No. A survey of one flat cannot prove a shared stack, the vent, or the neighbour’s appliances. Gurgling is a symptom you may hear or be told about. It is not a test, not a camera, and not a decision about who repairs the 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?

Stacks in blocks serve more than one home. When one WC pulls air through another trap, the cause may be a blocked vent, a partial obstruction, or a fitting that was altered. The surveyor inside this flat sees this pan and, if they are lucky, a boxed duct. They do not enter the flat above, and they do not open the whole riser. Approved Document H does not become a block survey because a trap gurgled. No drain-camera grade should be written. None was commissioned with the ordinary inspection.

Who pays for a shared stack is a lease and managing-agent question. The survey does not award that cost, and it does not turn a gurgle into a condition rating for the whole building. Ask the agent whether other flats have complained, and tell your solicitor. A drainage firm would need access beyond this room to prove the stack. Until then, say what this flat did: the pan gurgled, the stack was not seen, the survey stopped at the demise. Do not copy a “who repairs a soil pipe” answer onto a noise you have not traced.

What should you ask your surveyor?

Did you hear the gurgle yourself, or was it reported?
Could you see any of the shared stack from this flat?
Are you limiting the finding to this flat?

What are the typical next steps?

Ask the managing agent whether the stack has a known complaint.
Do not instruct work to the riser from inside one room.
If someone cameras or opens the stack, they need access the survey of this flat did not have.

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

Does a new pan in this flat prove the stack is clear?

No. The pan is yours to see. The shared pipe is not.

Is gurgling the same as a silted chamber in a garden?

No. This is a flat stack you could not follow. A garden chamber is a different inspection.