Drainage and septic tanks
The report places a Belfast sink, a bottle trap and a waste that falls the wrong way in one paragraph. Which of those were inspected, and which were merely named?
The Belfast sink and the bottle trap were inspected where they could be seen. The waste that falls the wrong way was judged by eye, not by running water, so it was looked at rather than tested. A bottle trap is the compact trap under the sink, and a wrong fall means the waste slopes back toward the sink or lies flat. The survey has not flow-tested that pipe and has not decided the sink will not empty. Boxed-in lengths, if any, were only named. The paragraph is not a drainage test.
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?
A Belfast sink is a deep ceramic sink, and the bottle trap under it holds a water seal against smells. The waste after the trap should fall toward the stack. If the visible pipe runs the wrong way, water can sit in the trap or drain sluggishly, but you confirm that by running water, which this visit did not. The surveyor sees the sink, the trap and the slope of the pipe that is in view. The wrong fall is a visual comment on the exposed waste.
Ask a plumber or a drainage firm to run water through the Belfast sink and correct the fall if the trial confirms it. The survey has not done that trial and has not specified the new pipe. Tell the solicitor the slope was seen and not tested, so do not describe the waste as blocked. A bottle trap can also be removed and cleaned, which is separate from the fall. Keep the sink, the trap and the slope as three notes, and keep any hidden length unknown.
What should you ask your surveyor?
- How much of the waste was visible, and how much was boxed in?
- Did the wrong fall start at the bottle trap or further along the run?
- Was any water actually run through the Belfast sink?
What are the typical next steps?
- Treat the sink and trap as seen, and the fall as a visual comment only.
- Have water run through the waste before anyone describes it as blocked.
- Tell the solicitor hidden lengths of pipe were not tested.
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 bottle trap the wrong sort of trap under a Belfast sink?
Not as a finding here. A bottle trap is a recognised compact trap. The survey saw it under the Belfast sink and did not say the type was the defect. The defect noted is the waste falling the wrong way, and even that was not flow-tested. Do not replace the trap merely because of its shape. The slope is the separate point.
Does the wrong fall mean the stack is blocked?
No. A pipe that slopes the wrong way is a local laying fault on the waste that was seen. A blocked stack would need a drainage inspection this visit did not do. The survey has not decided the stack is obstructed. Keep the visible fall separate from any guess about the soil pipe further on.