Drainage and septic tanks
Mushroom caps of a soakaway show in the lawn and were not lifted. What chamber, if any, sits under them?
No chamber can be named, because the mushroom caps were not lifted. They show in the lawn as the vents or markers of a soakaway, and what sits under them was not seen. There may be a chamber, a rubble-filled arm, or only a vent on a pipe. The survey did not establish which. It records the caps. It has not described a chamber beneath them and has not inspected the soakaway.
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?
Mushroom caps are the domed covers often used to vent a soakaway rather than to give a full inspection opening. Until a cap is lifted by someone equipped to do it, you cannot see depth, silt, collapse or whether a proper chamber exists at all. The lawn around them is not evidence of the void below. The survey only records what was seen, which is the caps on the surface. A cesspool, a septic tank and a treatment plant are different again, and these caps do not identify those vessels.
Ask the solicitor for any drainage plan that marks the soakaway, and for the tank or plant papers if the system is private treatment rather than a public sewer. A specialist can lift the caps and report what is there. Do not invent a legal distance from the caps to the house or a ditch. The home survey has not measured one and has not named a chamber. Keep any later drainage report separate from this note.
What should you ask your surveyor?
- Where in the lawn are the mushroom caps recorded?
- What sentence says they were not lifted?
- Does the report name a chamber, or only the caps?
What are the typical next steps?
- Treat anything under the caps as unseen.
- Ask for a drainage plan of the soakaway.
- Have a specialist lift the caps if the chamber must be known.
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 the number of caps tell you the soakaway’s size?
No. A count of mushroom caps on the lawn is not a volume and not a plan of the arms. The caps were not lifted, so the survey cannot say what chamber, if any, sits under them. Size, silt and condition stay unknown. The report records the caps it could see and stops there.
Were these caps the emptying point of a cesspool?
The visit did not establish that. A cesspool holds sewage and is emptied, usually at a different cover from a soakaway vent. These are described as mushroom caps of a soakaway, and they were not lifted. The survey has not identified a chamber under them and has not called them a cesspool emptying point.