Drainage and septic tanks
What is a septic tank, in the words government guidance uses for buyers in England?
Government guidance describes a septic tank as a system that treats sewage and then releases liquid into the environment, typically into the ground through an infiltration system. It is not a mains sewer. A home survey can note that a tank exists if the surveyor can see it. It does not prove the tank meets the general binding rules.
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 same guidance says you are the operator if you own the property that uses the system, if you share it, or if your tenancy makes you responsible. After completion that becomes you. The rules in England depend on whether the discharge is to ground or to surface water, and on whether the system is an existing discharge or a new one. The page also says Scotland, Wales and Northern Ireland have different rules. This answer does not invent those rules.
Ask the seller, through the solicitor, where the tank discharges, when it was installed, and when it was last emptied. Ask the surveyor what they could see: a cover in the garden is not a drainage field. If you need to know whether it complies, ask a competent drainage installer and read the official pages. Compliance work, if any, is their quote.
What should you ask your surveyor?
- Did you see a tank, a treatment plant, or only the absence of a mains connection?
- Could you see where the liquid goes, or was that hidden?
- Are you able to say the system meets the general binding rules? A visual survey should not pretend to.
What are the typical next steps?
- Get the discharge point and the last emptying invoice from the seller.
- Read the official septic-tank pages before you price a replacement.
- Tell your solicitor if there is no mains connection. Searches may not spell out the tank.
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 the same as a septic tank?
No. A cesspool stores sewage and must be emptied. It does not treat and discharge in the way the septic-tank pages describe. Ask the surveyor which one they think they saw, and ask an installer to confirm.
Does a survey smell test the tank?
A smell is a clue. It is not a compliance check and it is not a sample of the discharge.