The short answer
A building survey covers the visible and accessible parts of the drainage system but is not a drainage survey. The surveyor will, where chambers are accessible, lift inspection covers, look into the manhole for flow, blockages, root ingress and damaged benching, note the gullies, soil and vent pipes, and report on a visible septic tank or treatment plant and its general condition. What they cannot do is run a camera down the pipe runs, perform a flow or watertightness test, or confirm the condition and compliance of an underground septic tank. Because below-ground pipes and tanks are out of direct view, the report recommends a CCTV drain survey — and, for off-mains drainage, a septic tank inspection against the current rules — where there is doubt.
Drainage problems are expensive and hard to see. Here is how a building survey treats drains and septic tanks, and why a specialist follow-up is so often advised.
Drainage check at a glance
- CoversVisible chambers, gullies, pipes
- Septic tankVisible parts and general condition
- Not doneCCTV, flow test, tank emptying
- Off-mains ruleGeneral Binding Rules apply
- Next stepCCTV drain / septic inspection
What the surveyor checks at the surface
Above ground, the surveyor follows the drainage as far as it can be seen. They note the soil and vent pipes, rainwater downpipes and their connections, gullies and channels, and — where covers can be lifted safely — they look into inspection chambers (manholes) to check the benching and channels, the flow of water, standing water suggesting a downstream blockage, root ingress, and signs of collapse or displaced joints. They will report whether the property appears to be on mains drainage or has private/off-mains drainage such as a septic tank, cesspool or package treatment plant. Heavy, sealed or buried covers may prevent access, in which case the chamber is recorded as not inspected.
Septic tanks and off-mains drainage
If the property is not on the public sewer, the drainage becomes the owner's responsibility and is governed by the General Binding Rules in England (with parallel rules elsewhere in the UK). A building survey can describe a visible tank or treatment plant and obvious problems, but cannot confirm capacity, condition below ground, or whether the discharge is compliant. That matters because a tank discharging directly to a watercourse may need to be replaced or upgraded, which is a meaningful cost and a legal liability passing to the buyer.
| Item | Building survey can | Specialist needed for |
|---|---|---|
| Manhole chambers | Lift lid, view flow if accessible | Sealed/buried chambers |
| Underground pipe runs | Note visible defects | CCTV camera survey |
| Septic tank | Describe visible parts | Condition, capacity, compliance |
| Discharge / soakaway | Note obvious issues | Compliance with binding rules |
Indicative scope; off-mains drainage often warrants its own inspection. Sources: gov.uk General Binding Rules; RICS.
When to commission a CCTV drain survey
Because the surveyor cannot see inside the pipe runs, a CCTV drain survey is the standard follow-up where there is reason to be concerned: evidence of past blockages or slow drainage, root ingress at a chamber, large trees near the runs, a property with a history of flooding, or simply an older property where the drains have never been checked. The camera reveals cracks, collapses, displaced joints, root masses and shared or mis-connected runs that no surface inspection can confirm. For off-mains properties, a septic tank inspection against the current rules is the equivalent step, ideally before exchange so any upgrade liability is known and can be reflected in the price.
Frequently asked questions
Does a building survey include a CCTV drain survey?
No. A building survey checks visible chambers and pipes and reports their apparent condition, but it does not put a camera down the runs. A CCTV drain survey is a separate specialist inspection that the report may recommend.
Will the surveyor inspect the septic tank?
Only the visible parts and obvious condition. They cannot confirm the tank's underground condition, capacity, or whether its discharge complies with the General Binding Rules. A dedicated septic tank inspection is needed for that.
Why does off-mains drainage matter when buying?
Because the buyer takes on the tank as a liability. A non-compliant tank — for example one discharging straight to a stream — may legally need upgrading, which is a real cost worth confirming before exchange.
Sources & further reading
- gov.uk — septic tanks and treatment plants (General Binding Rules)
- HomeOwners Alliance — property surveys explained
Figures on this page are typical UK ranges drawn from published sources and depend on the specific property and survey level. They are guidance, not a quotation.