CLEARMASTERS
The short version
How often does a septic tank need emptying?
A septic tank needs emptying at least once a year, and the general binding rules require it to be done before the sludge reaches its capacity. A treatment plant is usually desludged about once a year too. A cesspit stores everything, so it needs emptying far more often: typically every few weeks to every couple of months, depending on its size and your water use.
Interactive
Emptying estimator
Answer a few questions to see how often yours is likely to need emptying, and when it’s next due.
At a glance
Typical emptying intervals
| System | How often | Why |
|---|---|---|
| Septic tank | At least once a year | Solids settle as sludge and must be removed before they wash out to the drainage field. Required by the general binding rules. |
| Treatment plant | About once a year, plus a service | Sludge builds up in the primary and settlement chambers. Too much and the plant stops treating properly. Check the maker’s guidance. |
| Cesspit | Every few weeks to months | A sealed tank with no outlet, so it fills at the rate you use water. |
| Pump station | Service once or twice a year | Fat, wipes and silt build up in the chamber. Our pump station guide explains more. |
We empty all of these with our own tankers, and you get a waste transfer note every time.
Interactive
What happens if you leave it too long?
Drag the slider to see a septic tank fill with sludge over time.
A septic tank works by giving solids time to settle. As sludge builds up, that time shrinks, until solids flow straight through. Our guide to drainage field problems explains what happens next.
Your system
What affects how often it needs emptying?
How many people
More people means more solids and more water. Sludge builds up roughly in line with the number of people.
Tank size
Older tanks are often smaller than today’s minimum of 2,700 litres for four people, so they fill faster.
Water use
The biggest factor for a cesspit. Leaking taps and toilets add up fast.
Rain and groundwater
Gutters, drives or cracked pipes letting water in will fill a cesspit and wash sludge out of a septic tank.
Kitchen waste
Waste disposal units, fat and food scraps add solids that don’t break down.
Chemicals
Bleach and harsh cleaners kill the bacteria that break the sludge down. See what not to flush.
Busy spells
Holiday lets and guests mean more people for short periods.
Age and condition
Cracked baffles or a missing T-piece let scum and sludge escape, whatever the interval.
Warning signs
Signs your septic tank needs emptying
Don’t wait for these. By the time you notice them, solids may already be reaching the drainage field. But if you see them, book an emptying soon.
A bad smell is one of the most common signs. Our guide to septic tank smells helps you work out where it’s coming from.
For a cesspit, the high-level alarm or the liquid nearing the inlet pipe is your cue.
Cesspits
How to make a cesspit last longer between emptyings
Do
- Fix dripping taps and running toilets straight away
- Fit dual-flush toilets, aerated taps and low-flow showers
- Run full loads in the washing machine and dishwasher
- Keep gutters and drive drains away from the cesspit
- Fit a high-level alarm so you get warning
Don’t
- Let rainwater or groundwater in
- Ignore cracks: a leaking cesspit can let water in or sewage out
- Wait for the alarm before booking
- Connect new bathrooms without checking the tank size
If you’re emptying very often, a treatment plant can cut emptying to about once a year where there’s somewhere for the treated water to go. See cesspit emptying or ask our team.
Be ready
What happens on the day
Clear the way
Tell us about gates, codes, low branches and narrow lanes so the right tanker comes.
Find the lids
Make sure the lids aren’t buried, locked or under pots and decking.
Hose distance
Let us know roughly how far the tank is from where a tanker can park.
Emptying
We remove the sludge, scum and liquid, and check the tank for obvious problems.
Paperwork
You get a waste transfer note: keep it as proof the tank has been emptied.
Questions answered
Septic tank emptying FAQs
How often should a septic tank be emptied?
At least once a year for most homes. The general binding rules require the sludge to be removed before it reaches the tank’s capacity, at least once a year or as often as the manufacturer recommends. A small tank, a large household or a waste disposal unit can mean emptying more often.
How often does a cesspit need emptying?
It depends on its size and how much water you use, because a cesspit holds everything. For a family it’s typically every few weeks to every couple of months. Divide the tank’s capacity by your daily water use for a rough guide, or use our estimator.
How often should a sewage treatment plant be desludged?
Most treatment plants need desludging about once a year, as well as an annual service, but some models need it more or less often. Follow your manufacturer’s guidance.
What happens if a septic tank is not emptied?
The sludge builds up until there isn’t room for solids to settle. They then flow out with the liquid into the drainage field and block the soil, which can lead to smells, soggy ground, backed-up drains and an expensive replacement soakaway.
Can a septic tank be emptied too often?
Emptying more often than needed does no harm to the tank, but it costs you more. Leaving a little sludge behind helps it get going again. We measure the sludge at each visit and will tell you if you can go longer between emptyings.
How do I know when my septic tank needs emptying?
Slow drains, gurgling, smells, wet or lush patches over the drainage field, or simply not knowing when it was last done are all signs. The surest way is to have the sludge level measured.
How big is my septic tank?
The size is often on the lid, in the property paperwork or on a previous emptying receipt. Under Building Regulations a new septic tank must hold at least 2,700 litres for up to four people, plus 180 litres for each extra person.
Do I need to be home when the tank is emptied?
Not usually, as long as we can get to the tank and the lids aren’t locked or buried. Let us know about gates, access codes, pets and where the tank is.
Got a different question? Call 03333 233566 or send us a message.