Drainage and septic tanks
What is a cesspool, and how is it different from the septic tank GOV.UK describes?
GOV.UK describes a septic tank or treatment plant as a system that treats sewage and releases liquid to the environment. A cesspool stores sewage and does not treat it. It has to be emptied. A cover in the garden does not tell a surveyor which one is in the ground.
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?
The difference matters because the rules for a discharge are not the rules for a sealed tank. England’s general binding rules, in force from 2 October 2023, are about small sewage discharges. A tank that only stores sewage is a different operation, with an emptying cost nobody can see from the manhole cover. A visual survey may record a cover and a seller’s label. It does not trace the outlet or measure the tank.
Ask the seller what the system is, who empties it, and where any outlet goes. Ask your solicitor to match that to the searches. If the survey could not lift the cover, say so. There is no national emptying price in the RICS guide. Ask a local contractor for a quote once you know the volume and the access. Do not assume a septic tank is a cesspool because the garden is rural.
What should you ask your surveyor?
- Could you tell a cesspool from a septic tank or a treatment plant, or only see a cover?
- Did you find an outlet, or was the outfall not visible?
- What should we ask the seller to produce: emptying invoices, or a description of the discharge?
What are the typical next steps?
- Get the seller’s description in writing and compare it with any invoice.
- If you need to know where the liquid goes, instruct a drainage inspection. Do not guess from the wildflowers.
- Budget emptying only after you know it is a cesspool. A treatment plant has running costs of a different kind.
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 allowed to overflow to a ditch?
A storage tank that overflows is discharging. GOV.UK’s rules for discharges in England are the ones to read, not a neighbour’s habit. Ask the solicitor if that is what the seller describes.
Can the surveyor measure how often it must be emptied?
No. Frequency depends on use and volume, which the inspection has not measured.