How much does it cost to install a septic tank?
The tank is the cheap part. The digging, the drainage field and the paperwork are where the money goes.
Installing a septic tank typically costs £4,200 to £6,000, according to Checkatrade. That covers the tank, installation and standard excavation. MyJobQuote’s average is about £5,500. A difficult site or a new drainage field can push the total past £10,000.
Quick answer
- Installed, typical
- £4,200–£6,000 (Checkatrade); average about £5,500 (MyJobQuote)
- Tank only
- £1,200–£1,800 (Checkatrade); £800–£1,500 (MyJobQuote)
- Replacement
- Around £4,000 if the drainage field still works (Checkatrade)
- New drainage field
- £3,000–£7,000 (Checkatrade); £1,500–£4,000 (MyJobQuote)
- Time on site
- About 2–7 days below ground
Prices checked November 2026, from Checkatrade (updated April 2026) and MyJobQuote (updated September 2026). Ballpark figures, not quotes.
Installed prices by tank size
Two cost guides, two sets of numbers. Use both as a range, not a quote.
| Tank | Checkatrade (excavation + tank) | MyJobQuote (installed, incl. drainage field) | Time (MyJobQuote) |
|---|---|---|---|
| Small | £4,200 | £2,500–£5,000 | 2–4 days |
| Medium | £5,000 | £4,500–£7,000 | 3–5 days |
| Large | £6,000 | £7,000–£10,000+ | 5–7 days |
Checkatrade splits its figures into excavation (£2,720 to £3,905) and the tank and positioning (£1,500 to £2,100). It assumes easy access for machinery, standard excavation and a typical domestic property. MyJobQuote’s prices include the tank, excavation, labour, pipework and drainage field installation.
Where the money goes
MyJobQuote breaks a typical job down like this:
| Item | Typical cost |
|---|---|
| Septic tank unit | £800–£1,500 |
| Site survey and percolation test | £250–£500 |
| Excavation and groundwork | £500–£1,500 |
| Drainage field materials and installation | £1,000–£3,000 |
| Labour | £300–£1,750 |
| Concrete surround or base (if required) | £300–£800 |
| Soil removal and disposal | £200–£600 |
| Ground reinstatement | £200–£800 |
| Permits and building control approval | £150–£400 |
Checkatrade prices the tank alone at around £1,200 (small) to £1,800 (large), before any digging.
Replacing an old septic tank
Checkatrade says replacing a septic tank usually costs around £4,000, particularly if the drainage field can still be used. If the old system has contaminated the soil or the field has failed, costs climb:
- New compliant drainage field: £3,000 to £7,000 (Checkatrade); £1,500 to £4,000 (MyJobQuote)
- Replacing a failed drainage field: £1,500 to £5,000 (MyJobQuote)
- Contaminated soil removal: about £40 per cubic metre (both guides)
Not sure your field has failed? Check the warning signs first.
What pushes the price up
Checkatrade lists the main cost drivers:
- Tank size. Bigger tanks cost more but usually need emptying less often.
- Ground conditions. Rocky soil, clay or high groundwater slow the dig.
- Access. Narrow access, steep gardens or tight space add labour.
- Drainage. Some properties need a new drainage field or upgrades to meet current rules.
- Location. Costs are often higher in London and the South East.
MyJobQuote adds that clay-heavy or waterlogged soil may rule out a drainage field entirely. Then a sewage treatment plant may be needed instead, at £6,000 to £12,000 installed by its figures. Our treatment plant cost guide has more.
Need a price for your property? Ask at least three local firms for a written quote. Our directory lists checked firms in Devon, Cornwall, Norfolk, Herefordshire and Shropshire.
Find local firmsThe rules a new septic tank must meet (England)
Price is only half the job. A new system has to be legal, too.
Sewer first. Gov.uk says a new discharge must connect to a public foul sewer if the Environment Agency decides it’s reasonable. It weighs how close the sewer is, the cost of connecting compared with a treatment system, physical barriers such as a large road, and any environmental benefits.
Approval. You must have Building Regulations approval to install a new sewage treatment system. You might also need planning permission. Check with your council.
Ground, not water. Under the general binding rules, a septic tank must discharge to ground through a drainage field. To discharge to a watercourse, you need a small sewage treatment plant. See septic tank vs treatment plant vs cesspit.
Standards and sizing. New tanks must meet BS EN 12566, and drainage fields BS 6297:2007. Gov.uk says you must check with the installer that a new system meets the sizing requirements in British Water’s Flows and Loads guidance.
Location checks. A new discharge to ground needs a permit, rather than the general binding rules, if it’s within 50 metres of another system discharging under those rules. You also need a permit if the discharge point is in a groundwater source protection zone 1 (except SPZ1c), or if the discharge is in or within 50 metres of certain protected sites such as an SSSI.
These rules are for England. Scotland and Wales have their own regulators, SEPA and Natural Resources Wales.
Getting quotes
Checkatrade suggests checking that a quote covers tank supply, excavation and installation, waste disposal, ground preparation, drainage connections, any extra equipment, the timeline and the total including VAT. If one quote is much cheaper, check what it leaves out. It may not cover excavation, disposal or compliance work.
FAQ: septic tank installation costs
How much does it cost to install a septic tank in the UK?
Checkatrade puts a typical installation at £4,200 to £6,000, including the tank and standard excavation. MyJobQuote gives an average of about £5,500, with large tanks at £7,000 to £10,000 or more. Complex jobs with significant groundwork or a new drainage field can exceed £10,000, says Checkatrade.
How much does it cost to replace a septic tank?
Checkatrade says around £4,000, particularly if the existing drainage field can still be used. A failed drainage field adds to that: Checkatrade puts a new compliant one at £3,000 to £7,000.
Do I need permission to install a septic tank?
In England, gov.uk says you must have Building Regulations approval for a new septic tank or small sewage treatment plant, and you may need planning permission. A new discharge must connect to the public sewer if the Environment Agency decides that's reasonable.
Can a new septic tank drain into a stream?
Not in England. Under the general binding rules, a septic tank must discharge to ground through a drainage field. To discharge to a watercourse you need a small sewage treatment plant instead.
How long does a septic tank installation take?
Checkatrade and MyJobQuote both say around 2 to 7 days for a below-ground system and about a day for an above-ground system. Surveys, approvals, ground conditions and weather can add time.
Sources
All links checked October 2026.
- Checkatrade: Septic tank installation and replacement cost in the UK (2026 guide), updated April 2026
- MyJobQuote: How much does it cost to install a septic tank? (last updated 28 September 2026)
- GOV.UK: Your property has a new discharge
- GOV.UK: General binding rules, small sewage discharge to the ground
- GOV.UK: General binding rules, small sewage discharge to a surface water
We write plain-English guides for UK homes that are not on mains sewers. Every rule links to the regulator. Every price links to where we found it. About us · How we check costs.