Drainage and septic tanks
The septic tank lid is buried in the lawn and was not found. What do you know?
You know the survey did not find a lid to open. You do not know the tank type, the condition, or where the outfall goes. Grass over a possible tank is not an inspection. The survey does not prove the outfall.
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?
From the lawn alone you cannot tell a septic tank from a treatment plant or a cesspool. A cesspool stores sewage and does not discharge. A septic tank and a treatment plant are different again, and in England the general binding rules for small discharges are not something a surveyor proves by walking the grass. Wales, Scotland and Northern Ireland differ, so do not apply the English rules as if they were universal. The visit did not dig, and a standard inspection does not lift chamber covers that it cannot find. Approved Document H does not locate a buried lid.
Ask the seller where the lid is, when the tank was last emptied, and where they believe the effluent goes. Those answers are leads, not a survey. If nobody can find the lid, you cannot look inside before exchange unless someone agrees to uncover it. Do not drive probes at random. A drainage firm who knows private systems can advise once there is a lid or a plan. There is no camera grade to quote, because no camera was used. Keep this separate from a tank the survey found but could not open. Here the point is that the lid was not found.
What should you ask your surveyor?
- Did you find any lid, vent, or marker, or was the lawn uninterrupted?
- Are you avoiding a guess at septic tank, treatment plant, or cesspool?
- What should the seller be asked to show us so the lid can be found?
What are the typical next steps?
- Ask the seller to mark the lid. Do not excavate the lawn yourself.
- Do not assume an outfall the survey could not see.
- If the lid is uncovered later, look then. Today’s report stops at “not found”.
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 green strip in the grass prove the tank is there?
No. It is a clue at most. The survey did not find metal or concrete to open.
Is a cesspool allowed to discharge because the lid is missing?
No. A cesspool stores sewage and does not discharge. A missing lid does not change that, and it does not prove which tank this is.