Drainage and septic tanks
A septic tank is described and the soakaway could not be found. What part of the system is still unknown?
The soakaway, and the route effluent takes after the tank, is still unknown. A septic tank is described, but the soakaway that should take liquid from it could not be found, so the trenches and the ground they discharge into were not seen. A septic tank and a treatment plant are different things, and a cesspool only holds sewage until it is emptied. The survey recorded the tank it could describe and the missing soakaway. It has not mapped the rest of the system or decided that it works.
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 septic tank settles solids and should pass liquid onward. If the onward part cannot be found, the survey cannot say whether liquid soaks into the ground, backs toward the tank, or leaves the site some other way. Covers that were seen do not stand in for pipes that were not traced. The visit did not dig the garden and did not dye-test a discharge. Emptiness or a recent desludge, if anyone claims one, was not proved by finding the soakaway.
Ask the solicitor for emptying records, any consent or exemption, and any plan that marks the soakaway, and keep those papers off the survey text. A drainage firm can trace the outfall if you instruct them later. Tell a lender the tank was described and the soakaway was not found, so the discharge route is unknown. Do not describe the system as complete because a tank was on the plot.
What should you ask your surveyor?
- Was the soakaway found, or only the tank described?
- Did this visit trace the pipe that should leave the tank?
- Are emptying notes and any consent still outside this report?
What are the typical next steps?
- Treat the discharge route after the tank as unknown.
- Ask the solicitor for plans, consents and emptying records.
- Instruct a drainage firm only if you need the outfall traced.
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 cesspool what this report has described?
No. The report describes a septic tank, which is not a cesspool and not a treatment plant. A cesspool holds sewage and is emptied. A septic tank is meant to pass liquid onward, and here that onward soakaway was not found. The survey has not reclassified the tank. It has only said the rest of the system was not seen.
Does a lid in the lawn prove the soakaway is there?
A lid proves a lid. It does not prove a working soakaway, a set of trenches, or a clear outfall. The survey could not find the soakaway and did not dig for it. Do not promote an unidentified cover into a drainage field. Any later tracing is new work, and it should be reported on its own papers.