Since the General Binding Rules came into force (2015, tightened January 2020), a septic tank that discharges to a ditch, stream or any watercourse is not legal to operate — it must have been replaced or upgraded by 2020. Plenty of Cornish systems still haven't been, and owners typically discover this during a house sale, when the buyer's solicitor asks for drainage paperwork nobody has.
Work through the checklist below. It takes about five minutes if you know your system, and it covers what a buyer's conveyancer — or the Environment Agency — would ask.
The checklist
Ticked everything? Good — stay that way
Keep emptying on schedule (what it costs), keep the receipts, and re-check after any building work or change of use — a granny annexe or holiday-let conversion changes the loading on the system.
Couldn't tick something?
Not sure what you have or where it discharges: a CCTV drain survey (£150–£250) answers it definitively — cheap certainty compared to guessing wrong in a sale.
Discharging to a watercourse: you'll need an upgrade — usually a treatment plant or a new drainage field. Costs range £3,000–£15,000 depending on the fix; see the installation guide. There's no grace period left; this was due by January 2020.
Failure signs: start with diagnosis and repair — most "failed" systems are a saturated soakaway, not a dead tank.
Not sure where you stand? Ask for an introduction
Leave your postcode and we’ll try to introduce you to one local septic tank firm who can confirm what system you have, whether it complies, and what (if anything) needs doing. We’re still looking for local firms to work with, so we may not have one for your area yet. Whoever you use, check them on the Environment Agency’s public register of waste carriers.
Want the deeper background on the rules themselves — discharge volumes, permits, the 2015/2020 timeline? Read our full guide: The General Binding Rules, explained for Cornwall homeowners.