Cornwall has one of the highest concentrations of holiday lets in Britain, and a large share of them — coastal cottages, barn conversions, moorland hideaways — sit on septic tanks rather than mains drainage. That combination has a failure mode every experienced owner knows: the tank that was "fine last year" backing up in the second week of August with guests in the house.
Why holiday lets fill tanks so much faster
- Occupancy spikes. A 6-guest let at 90% summer occupancy puts two to three times the load of a normal household through the same tank. A tank sized for annual emptying under family use can need emptying every 3–6 months under holiday load.
- Guests don't know they're off-mains. Wipes, sanitary products and cooking fat go down the drain because nobody told them not to. These are the top causes of blockages and soakaway damage in Cornish lets.
- Nobody's watching the tank. Owners are often up-country, and cleaners aren't checking sludge levels between changeovers. Problems announce themselves mid-stay instead of being caught early.
How Cornwall owners handle it
| Approach | What it looks like |
|---|---|
| Pre-season empty | Tank emptied March–April before bookings ramp up. The single highest-value visit of the year. |
| Changeover-day scheduling | Tanker visits between departure and arrival — guests never see it. Book these slots ahead; Fridays and Saturdays go first. |
| Mid-season check | For high-occupancy lets: a quick level check (or second empty) in July–August heads off the classic peak-season backup. |
| Guest-proofing | A polite bathroom notice ("we're on a septic tank — nothing but loo roll, please"), a kitchen fat trap, and bins in every bathroom. |
The cost of getting it wrong
A routine planned empty costs £150–£300 (see the full Cornwall price guide). A mid-stay backup costs an emergency callout plus whatever the ruined stay costs you — refunds, relocation, and the review that mentions sewage. Owners who've had one August emergency become permanent advance-bookers.
Compliance matters more for lets
Your septic system must meet the General Binding Rules — and for a business asset (which a holiday let is), non-compliance carries more risk than for a private home: it surfaces in property sales, insurance claims and, increasingly, letting-agency onboarding. Run through our 5-minute compliance checklist to see where you stand — most owners pass; the ones who don't are usually one fixable item away.
Holiday-let hotspots
Holiday lets cluster in a few hotspots, each with its own town guide: St Ives & Carbis Bay, Newquay & Mawgan Porth, Wadebridge, Rock & Polzeath, St Austell, Mevagissey & Charlestown, Falmouth & the Helford, and the Lizard.
Get it sorted before peak season peaks
Find a local firm that works around holiday lets and check it on the Environment Agency’s public register of waste carriers, or ask us for an introduction (we’re still looking for local firms to work with, so we may not have one for your area yet). Either way, tell them the property, rough occupancy, and when your changeover days fall.
Common questions
How often should a holiday let septic tank be emptied in Cornwall?
A fully-booked holiday let works a septic tank two to three times harder than normal household use. Most Cornwall holiday lets on standard 2,700-litre tanks need emptying every 3–6 months during the season, versus annually for a normal household. Occupancy is the driver — a 6-guest property at 90% summer occupancy may need a mid-season empty.
Can septic tank emptying be scheduled around changeover days?
Yes — this is the standard way to service Cornwall holiday lets. The tanker visits between guest departures and arrivals so guests never see the work. Book ahead in peak season, as changeover-day slots (especially Fridays and Saturdays) fill quickly.
What happens if the septic tank backs up while guests are staying?
Treat it as an emergency — a backed-up tank mid-stay usually means refunds or relocations. Ring two or three local firms straight away; same-day emptying is sometimes possible when a firm has capacity. Better: a pre-season empty and a mid-season check make mid-stay failures rare.
Do guests cause septic tank problems?
The classic holiday-let failure is wipes, sanitary products and kitchen fat from guests who don't know (or don't think about) the property being off mains drainage. A polite bathroom notice and a fat-trap in the kitchen prevent most of it.