What do you need?
Septic tank replacement
Cracked, leaking or non-compliant tank? See the signs, the rules and typical costs.
New septic tank installation
Self-builds, conversions and off-mains homes: percolation tests, approvals and sizing.
Sewage treatment plants
Needed for most watercourse discharges and poorly draining ground.
Typical costs at a glance
These are guide prices from installers' published price guides and merchants' list prices, with each source linked. Your site will be priced on its ground, access and discharge route.
| Item | Typical cost | Source |
|---|---|---|
| Septic tank unit only, about 2,800–3,100 litres (5–6 people). Equipment only: no delivery offload, excavation or installation. | about £1,180–£1,220 inc VAT | Clarkes of Walsham; Tanks For Everything, Oct 2026 |
| Larger septic tank unit only, 5,000 litres. Equipment only. | about £1,890 inc VAT | Tanks For Everything, Oct 2026 |
| Like-for-like tank replacement, supplied and installed, where the existing drainage field can be kept | roughly £3,000–£7,000 | Alton Facility Services; Clear Stream Drainage Solutions |
| New drainage field (sized from a percolation test), supplied and installed | £3,000–£7,000; one installer advertises from £3,500 (1–3 bed) and from £4,500 (4+ bed) | Clear Stream Drainage Solutions; Fastfix Drainage & Plumbing |
| Percolation test | around £300–£500 | Clear Stream Drainage Solutions |
| New septic tank with a drainage field, supplied and installed | from about £5,500 on a straightforward site; commonly £5,000–£15,000 | Fastfix Drainage & Plumbing; Clear Stream Drainage Solutions |
| First-time installation or difficult site (rock, clay, high water table, poor access) | £12,000–£18,000 or more | Homebuilding & Renovating; Clear Stream Drainage Solutions |
| Item | Typical cost | Source |
|---|---|---|
| 6–7 person treatment plant, unit only: Marsh Ensign, Tricel Novo UK6, Graf One2Clean 7PE. Equipment only: excludes installation. | about £2,190–£2,700 inc VAT | Cotterill Civils; Tanks For Everything; Tanks For Everything, Oct 2026 |
| Premium 6-person unit: Klargester BioDisc BA. Equipment only. | about £4,950 inc VAT | Tanks Direct, Oct 2026 |
| Manufacturer's guide for the unit only | £1,700–£3,000 (6-person), £1,900–£3,500 (8-person) | Tricel |
| Installation on top of the unit (delivery, excavation, groundwork) | £2,000–£8,000, depending on size and ground | Tricel |
| Supplied and installed, typical domestic job | commonly £7,500–£15,000; difficult sites cost more | Fastfix Drainage & Plumbing; Alton Facility Services; The Sewage Guy |
| Annual service | about £100–£300 a year, plus any parts | Alton Facility Services; Fastfix Drainage & Plumbing; Tricel |
The rules where you live
- England: general binding rules from the Environment Agency. Septic tanks must not discharge to surface water. Read more
- Scotland: SEPA authorisation under EASR, which replaced CAR from 1 November 2025, plus a building warrant. Read more
- Wales: free one-off registration with Natural Resources Wales. Read more
- Northern Ireland: a consent to discharge from NIEA. Read more
How it works
We're upfront: we're an introduction service, not installers, and installers may pay us for introductions. How it works.
Areas we cover
We cover the whole UK. These guides focus on areas with lots of off-mains homes:
Scotland
England
Northern Ireland
Frequently asked questions
How much does a septic tank replacement cost?
Installers publish roughly £3,000–£7,000 for a like-for-like replacement where the drainage field can be kept. A new drainage field adds £3,000–£7,000, and difficult sites can exceed £12,000.
How much does a sewage treatment plant cost to install?
Units cost about £2,190–£2,700 inc VAT from merchants (equipment only). Supplied and installed, installers commonly quote £7,500–£15,000.
Are you installers?
No. Septic Tank Quotes is a free matching service. We pass your enquiry to up to 3 independent installers who cover your area.
Do I need permission for a new septic tank?
Yes. You need building regulations approval (a building warrant in Scotland) and the right environmental authorisation: the general binding rules or a permit in England, SEPA in Scotland, NRW in Wales, or NIEA in Northern Ireland.