What is a septic tank?
A septic tank is an underground tank that takes all the wastewater from a home that is not on the mains sewer. Inside it, the solids sink to the bottom and build up as sludge. The liquid on top flows out into a drainage field, a set of perforated pipes buried in the ground, where the soil does the rest. Gov.uk groups septic tanks and small sewage treatment plants together under the general binding rules for discharges to the ground.
- Waste in. Everything from your toilets, sinks, shower and washing machine runs down one pipe into the first chamber of the tank.
- Solids settle. Heavy solids sink and form sludge. Fats and lighter matter float as a crust. Bacteria break some of it down, but not all of it.
- Liquid to the drainage field. The settled liquid flows out to a drainage field in the ground. The sludge stays behind until a tanker removes it.
The tank only works if the sludge is taken away before it fills the chamber. Leave it too long and solids wash through into the drainage field, which is the expensive part to replace. That is why emptying is the one job every owner has to book. For the full mechanics, chamber by chamber, read how a septic tank works.
Septic tanks in the UK: who has one
Septic tanks serve properties that are not connected to a public sewer. Where there is no mains connection, the wastewater has to be dealt with on site, and the usual choices are a septic tank, a cesspit or a small sewage treatment plant. If your water bill has no sewerage charge, or the deeds or survey mention private drainage, you are probably one of them.
Our guide to off-mains drainage explains how the three systems compare and how to tell which one serves your property.
Septic tank rules in England (the general binding rules)
Most owners never need to speak to the Environment Agency. If your system meets the general binding rules, you are fine. These four points are the ones that matter in practice, each taken from the gov.uk guidance.
1. No permit if you meet the rules
“If you meet the general binding rules, you do not need a permit.” You only apply for a permit if you cannot meet them, and you might need to make changes to your system to comply. Source: gov.uk permits for septic tanks.
2. No discharge to surface water
A septic tank can no longer discharge straight into a stream, river, ditch or other surface water. If yours does, act as soon as possible: connect to a public foul sewer, replace the tank with a small sewage treatment plant, or install a drainage field. Plans should usually be in place within 12 months. Source: gov.uk surface water rules.
3. Have it desludged
You must get the sludge removed. Gov.uk says to do this “at least once a year or in line with the manufacturer’s instructions”, and the company that takes the sludge away must be a registered waste carrier. Source: gov.uk ground discharge rules.
4. Keep it in good order
Have the system maintained in line with the manufacturer’s instructions. If it is not in good working order, you must have it repaired or replaced. Source: gov.uk ground discharge rules.
Selling a property with a septic tank
You must tell the new operator in writing that a sewage discharge is in place, and pass on how the system should be maintained, the maintenance manual and any maintenance records you have. Older guidance used 1 January 2020 as a fixed date for upgrading tanks that discharge to surface water. The current guidance sets no fixed cut-off, so go by the “as soon as possible” rule above.
This page covers England. Scotland, Wales and Northern Ireland set their own rules through SEPA, Natural Resources Wales and DAERA. For the full legal background, read our guide to septic tank regulations in the UK.
Septic tank, cesspit or treatment plant?
Three systems get called “the tank”, and the emptying job is different for each. Knowing which one you have tells the carrier what tanker to send.
- Septic tank. Settles the waste and sends the liquid out to the ground through a drainage field. Only the sludge needs taking away, which is the “Empty my tank” job on our form.
- Sewage treatment plant. A small sewage treatment plant cleans the wastewater further, often using a pump or air supply. Gov.uk lists fitting one as a way to fix a septic tank that discharges to surface water. It still needs desludging. See sewage treatment plant emptying and servicing.
- Cesspit. A sealed holding tank with no outflow. Everything stays in until a tanker takes it away. See cesspit emptying for how that service works.
Who can legally empty your septic tank
Only a registered waste carrier may take your sludge away. Gov.uk is direct about it: “The company you use to dispose of your waste sludge must be a registered waste carrier.” The duty does not stop with the tanker firm. Under the waste duty of care code of practice, every householder has a duty to take all reasonable measures to hand household waste only to an authorised person. In practice that means checking the carrier holds up to date and valid upper tier registration.
That check takes two minutes:
- Ask for the number. Ask the company for its waste carrier registration number. Each carrier should have a registration number starting CBDU, followed by a set of numbers.
- Look it up. Search the number on the gov.uk register of waste carriers. Check the name matches and that the registration is upper tier and in date.
- Note it down. Write down the number and the date you checked. It is not a legal requirement, but the code of practice suggests recording the checks you make.
The same goes for a firm that knocks on your door or calls you unasked offering to empty the tank. The code of practice says you should check them too.
Our register lists 275 companies, each checked against the Environment Agency register by registration number. 275 of them held an in-date registration when we last checked on 06 March 2026. When you ask for quotes through this page, your request goes to carriers on that list, so the first check is already done. You can still look the number up yourself, and we would encourage it.
How often septic tanks need emptying, and what it costs
The legal wording on frequency is simple: have the sludge removed at least once a year or in line with the manufacturer’s instructions. Your tank’s manual may set its own interval, so read that first. If you have no manual and no records, book an empty now and ask the carrier how full the tank was. That gives you a baseline for next time.
The surest way to a fair price is two or three quotes for the same job. For typical price ranges and what pushes them up, see our septic tank emptying cost guide.
Find a septic tank emptying company near you
Pick your region or county to see the registered carriers listed there, with their registration details and contact information. Or search from the homepage for septic tank emptying near me.
How we check firms: every listing is matched to the Environment Agency waste carrier register by registration number. The method is set out on our homepage.