Drainage and septic tanks
What is a soakaway, and why should it not be taking foul water?
A soakaway is a pit or crate that lets rainwater seep into the ground. It is for surface water. Foul water from toilets and kitchens belongs in a foul drain, a septic system or a treatment plant. A home survey may see a downpipe disappearing into the ground. It cannot see the crate, and it cannot prove the ground will keep accepting water.
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?
Approved Document H covers rainwater and foul drainage as different jobs. A downpipe into a soakaway can be right. A toilet into the same hole is not. The surveyor sees the pipe at the wall. The buried part is a limit unless you commission a test. A soakaway that floods the path in heavy rain is a surface-water problem. It is not subsidence unless the house is also moving.
GOV.UK’s septic-tank rules are about small sewage discharges, not about a rainwater crate. Do not mix the two in a letter to the seller. If rainwater floods, ask a drainage firm about that system. If foul is in the wrong place, say so separately. There is no RICS price for a new soakaway. The ground conditions decide whether one can even be rebuilt.
What should you ask your surveyor?
- Which pipes go underground, and which discharge to a gulley you could see?
- Is any foul pipe involved, or only rainwater?
- Did the garden show flooding, or is that outside what you saw?
What are the typical next steps?
- Do not connect a washing machine to a rainwater soakaway because the gulley is nearby.
- If the path floods, photograph it in rain. A dry-day survey cannot show the overflow.
- Ask a drainage firm before you agree to “new soakaways” as a lump sum.
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 water butt a soakaway?
No. A butt stores a little rain. The overflow still has to go somewhere. The survey may not mention the butt at all.
Can a soakaway cause subsidence?
Concentrated water near a foundation can matter. The survey has not proved that unless the house is cracking and the water path is described. Do not assume it.