The short version
The calculator gives one number from two different models. In Scotland it uses Scottish Water’s published 2026–27 household tariff: scheduled £254.40, unscheduled £353.10, urgent £509.70 — or the actual cost if that is more. Everywhere else it uses a private-market model with a scheduled midpoint of £225, an unscheduled midpoint of £275 and an urgent midpoint of £360, scaled by tank size and access.
Scotland: the official tariff
Scottish Water is the statutory provider of household septic tank de-sludging in Scotland. For 1 April 2026 to 31 March 2027 the household charges are scheduled £254.40, unscheduled £353.10, and urgent £509.70 — or the actual cost if that is higher. The calculator uses these figures directly and labels the result as a Scotland estimate. Eligibility and booking are Scottish Water’s to define, so we point at their septic tank de-sludging page rather than restating their rules.
Rest of the UK: the private-market model
England, Wales and Northern Ireland have no published emptying tariff, so we model the private market. Checkatrade’s 2026 guide puts a typical job at £175–£312.50 with an average around £225; MyJobQuote’s range is about £150–£250 for most homes, one to two hours on site.
The model takes scheduled £225, unscheduled £275 and urgent £360 as midpoints, then applies size multipliers — 0.92 for about 2,800 L, 1.0 for about 3,800 L, 1.18 for about 4,500 L, 1.32 for 6,000 L or bigger — and access multipliers of 1.18 for awkward access and 1.28 for remote sites. The typical scheduled band starts at £175 and £312.50 and is scaled by the same multipliers; unscheduled and urgent jobs get a band of roughly plus or minus 18% around their midpoint. These are planning figures, not quotes.
VAT
Emptying a domestic septic tank or cesspool is generally zero-rated for VAT; emptying an industrial system is standard-rated. See HMRC’s guidance on VAT rates for different goods and services.
What we do not know yet
Honest limits. We do not yet have a first-party dataset of invoices, so the private-market numbers rest on published industry guides rather than our own records. We do not model outliers — a failed drainage field, blocked pipework, extra disposal volume, or an unusually long hose run can all move a real price well outside the band. Estimates are not quotes. For a real price, ask two local waste carriers, tell them the tank size and access, and confirm what the quote includes.
Sources
Key sources are Scottish Water 2026–27 household charges, Checkatrade 2026, MyJobQuote, GOV.UK’s general binding rules (England only), Natural Resources Wales, NI Water, and British Water’s Flows and Loads guidance for sizing. The full list with links is in the footer of every page.