If you're buying a Cornwall property with a septic tank, a standard RICS homebuyer's survey is not enough. Surveyors lift the lid, peer in, write "appeared to be in working order on the day of inspection", and move on. A genuine septic tank survey is a separate job — and on Cornwall properties, where off-mains drainage is the rule rather than the exception, it's one of the most useful pre-purchase checks you can commission. This guide explains what a proper survey covers, what it costs, and the red flags that should make you renegotiate or walk.
Why a standard homebuyer's survey isn't enough
RICS Level 2 and Level 3 surveys are property-wide inspections. The drainage section is a single paragraph in a 40-page report, based on a visual look at one or two access points. Surveyors aren't required to camera the pipes, percolation-test the drainage field, or assess General Binding Rules compliance — and most won't, because it's outside their remit and adds cost.
The result: hundreds of Cornwall buyers each year complete on properties with non-compliant systems, collapsing soakaways, or undersized tanks they didn't know about. Discovery happens 3–6 months in, when the first signs appear — and at that point, the seller is gone and the £5,000–£15,000 bill is yours.
What a proper septic tank survey covers
A competent drainage specialist will check these nine things:
1. Tank type and capacity
Septic tank, cesspit, or sewage treatment plant? Each has very different running costs (see our comparison guide). Capacity is calculated against household size using BS 6297 — a 4-person property needs at least 2,700 litres. Undersized tanks fill faster, need more frequent emptying, and overflow more easily.
2. Tank condition
Cracks in concrete, corrosion on steel, structural integrity of plastic. Many older Cornwall tanks are 1970s–80s concrete units that are reaching end-of-life. A good surveyor will note hairline cracks (still serviceable), wider fissures (repair needed), and any signs of structural failure (replacement only).
3. Inlet, outlet, and baffle integrity
Baffles slow incoming wastewater so solids can settle. When they fail, solids escape into the drainage field — and the field clogs years before it should. Damaged inlet or outlet pipes leak effluent into the surrounding ground, which is a regulatory issue as well as a smelly one.
4. Discharge type and General Binding Rules compliance
Where does the tank discharge to — a drainage field, a ditch, or a watercourse? Since 2020, direct discharge to watercourses is no longer permitted without an Environment Agency permit, and many older Cornwall properties still discharge to ditches without one. The seller is legally obliged to declare this on the TA6, but in practice many don't realise the issue exists. A surveyor traces the outflow — see our GBR 2020 guide for the implications.
5. Drainage field / soakaway condition
The drainage field is the most expensive part to replace (£2,000–£5,000) and the most likely to be at end-of-life. Soakaways are designed to last 20–30 years; many in Cornwall are older. The surveyor checks for soggy ground, smell, vegetation patterns that suggest saturation, and (ideally) does a percolation test on the surrounding soil.
6. Pipework — CCTV inspection
A CCTV drain survey through the system reveals root ingress, joint failures, cracks, and partial collapses. This is the single most useful diagnostic and should be standard for any pre-purchase septic survey. Costs £150–£250 on top of the visual survey, and worth every penny.
7. Records and permits
Has the seller kept emptying records? Waste transfer notes from licensed carriers form the paper trail proving the tank has been properly maintained. Does the property have an Environment Agency permit (if needed)? Is there a service contract for any treatment plant?
8. Access for emptying
Can a tanker actually reach the tank? Long farm tracks, narrow lanes, low gateways, and overhanging trees can all turn a routine empty into a costly job. Many Cornwall coastal properties have access that excludes standard tankers and requires a smaller (more expensive per-load) vehicle.
9. Compatibility with the property's current use
If you're buying a 2-bed cottage to convert into a 5-bed holiday let, the existing tank may not be sized for it. Holiday lets in particular need oversized systems to handle peak occupancy — see our holiday let guide.
What a septic tank survey costs in Cornwall
| Survey type | Typical cost | Notes |
|---|---|---|
| Visual survey only | £100 – £200 | Tank + accessible pipework, basic written report |
| Visual + CCTV | £250 – £450 | Recommended baseline for pre-purchase |
| Full compliance survey | £400 – £750 | Includes percolation test, GBR assessment, formal report |
| Pre-purchase + insurance grade | £500 – £900 | Most detailed; suitable for legal/mortgage submission |
For a £400k Cornwall property purchase, a £450 survey that flags a £15,000 soakaway issue is the highest-ROI spend in the whole transaction.
Cornwall-specific things to look for
- Coastal corrosion: Metal fittings on tanks within a mile of the coast corrode noticeably faster. Vents, brackets, and inspection covers are first to go.
- Granite / shillet ground (Bodmin Moor, Penwith): Poor percolation in granite-based soils means soakaways struggle. Look for surface staining and reed/rush growth above the drainage field — signs of saturation.
- Clay soils (mid-Cornwall): Worst for percolation. Drainage fields here fail faster than national averages — typically 15–25 years vs the 30-year design life.
- High water tables (Lizard, Penwith, coastal): Some properties have permanently saturated soakaway ground. The tank may have been jury-rigged with a pump or overflow to a ditch. Both are regulatory red flags.
- Holiday lets: A tank sized for 2 full-time residents will not cope with rotating groups of 8. If the property has been let for years, expect more wear.
- Old farm conversions: Beautiful, but tanks may be 50+ year-old brick-built units never designed for modern usage.
How to read the report
A good survey grades each issue. Look for:
- Grade 1 / Green / OK: No action needed. Normal wear.
- Grade 2 / Amber / Monitor: Issue exists but not urgent. Budget for repair in 1–5 years.
- Grade 3 / Red / Immediate: Active problem. Repair/replace before completion or build into the purchase price.
- Grade 4 / Critical: System non-compliant or failing. Full replacement likely needed. Renegotiate or walk away.
If the report uses no grading system, that's a flag in itself — a generic "appears to be in working order" report isn't worth much. Ask for specific findings with photographs.
Red flags — when to walk away
- Cesspit in a high-cost-to-empty location — running costs alone can be £2,000+ per year
- Direct discharge to watercourse without a permit — likely £8,000–£15,000 to remediate
- No drainage field at all (tank discharges direct to ground) — needs full system redesign
- Tank in a position that's now inaccessible (e.g., extension built over it) — replacement required and complicated
- Multiple failures: cracked tank + saturated soakaway + non-compliant discharge — full system replacement, £10,000+
- Seller can't provide any emptying records and tank shows neglect — unknown maintenance history is a real risk
None of these are deal-breakers if the price reflects them. But you must price them in before exchange, not discover them after.
Negotiating with the seller after a bad survey
Three normal outcomes when a survey turns up significant issues:
- Seller fixes before completion. Common for smaller issues (pipe repairs, partial soakaway works). Get the work done by a specialist of your choice, paid for by the seller via solicitor.
- Price reduction reflecting cost of remediation. Most common for major issues. Get 2–3 written quotes for the work, present the lowest as the deduction. Typically 60–80% of the quoted cost is accepted.
- Retention from completion funds. Solicitor holds back the remediation cost until the work is done post-completion. Cleaner than option 1, gives you control over which specialist does the work.
The septic survey is the leverage. Bring it to the table with photographs, the grading, and the quotes. Almost every Cornwall seller accepts some adjustment when faced with documented issues.
Booking a survey
Most Cornwall drainage specialists offer pre-purchase surveys. Allow 1–2 weeks from booking to receiving the report. If you're up against an exchange deadline, the CCTV-only option (1 day on site, 1–3 days for the report) is often enough.
Need a septic tank survey on a Cornwall property you're buying? Submit your postcode and we'll match you with a licensed specialist who handles pre-purchase work as standard.
Frequently asked questions
Is a septic tank survey worth it?
For any Cornwall property purchase, yes. A £250–£450 survey can flag issues costing £5,000–£15,000 to remediate. Even when nothing's wrong, the peace of mind and the maintenance baseline are worth the cost.
Can I rely on the seller's TA6 form?
Not entirely. Sellers must complete TA6 honestly, but many genuinely don't know the condition of their drainage system. The form is a starting point, not a substitute for a survey.
How long does a septic tank survey take?
Visual surveys take 1–2 hours on site. CCTV adds another hour. Full compliance surveys with percolation testing can take half a day. Reports typically arrive within 3–5 working days.
Can I do my own survey?
You can do a basic visual inspection — look at the tank lid, check for smells, look for soggy ground over the drainage field. But you can't camera the pipes, percolation-test the soil, or assess GBR compliance without specialist equipment and knowledge. For pre-purchase, professional is the only sensible option.
What if the survey turns up problems and I still want the property?
That's fine — just negotiate. A bad survey is leverage, not a stop sign. The septic system is replaceable; the property's location and character usually aren't.