What a cesspit actually is (and why it costs six times more than a septic tank)
- A cesspit is a sealed box with “no openings except for the inlet, access for emptying and ventilation”. No outlet, no treatment, no bacteria doing anything useful. It fills, you pay.
- The regulations demand 18,000 litres for 2 users, plus 6,800 litres per extra user — a family of four needs 31,600 litres. A septic tank for four needs 2,700.
- Nobody sets a legal emptying frequency. The trade's own estimates scatter from 2–4 weeks to 7–8 weeks, which tells you they are guessing at your household.
- At £175–300 a visit every four to eight weeks, a cesspit costs roughly £1,100–3,900 a year to own. That is the number that should decide it, not the purchase price.
- It must sit at least 7 m from any habitable part of a building and within 30 m of a vehicle access. If the tanker cannot reach it, it does not work.
Here is a requirement almost no British household has heard of. The Building Regulations, on any property that drains to one of these tanks: "Where a foul water drainage system from a building discharges to a septic tank, wastewater treatment system or cesspool, a durable notice shall be affixed in a suitable place in the building containing information on any continuing maintenance required to avoid risks to health." Approved Document H repeats it in a line: "1.68 A notice should be fixed within the building describing the necessary maintenance."
If that notice existed in the houses that change hands every year, the commonest question in British rural property would already be answered on a plate screwed to a wall.
To me a cesspit is something completely different to a septic tank, hence why I'm quite confused!
dlipner, forums.moneysavingexpert.comSo diagnose it yourself, and it takes two questions. Is there an outlet pipe? Northern Ireland Water is blunt: "Cesspools do not have an outlet pipe or drain." One pipe in, nothing out, and you have a cesspit. And how often does the lorry come? That tell beats every survey, because the two systems live on different calendars — one visit a year against one every few weeks.
We were told we had a septic tank when we bought a house. It needed emptying about every 4 - 6 weeks, so was not a septic tank.
SlopesOff, mumsnet.comThat owner worked out the truth from the invoice rather than from the tank. Nothing emptied every four to six weeks is treating anything.
Search “cesspit” in Britain and Google will offer you the Cambridge Dictionary. Five and a half thousand people a month ask what it is, and the best answer the internet has managed is a definition of the metaphor.
So here is the real one, and it is short. A cesspit — cesspool, same thing — is a sealed tank that holds sewage until a lorry comes. It does not treat. It has no outlet. The Building Regulations spell it out: “Cesspools should have no openings except for the inlet, access for emptying and ventilation.”
Everything else about a cesspit follows from that one sentence, including the bill.
The number that decides everything
Read those first two rows against the third. Approved Document H, paragraph 1.61, word for word:
“Cesspools should have a capacity below the level of the inlet of at least 18,000 litres (18m³) for 2 users. This size should be increased by 6800 litres (6.8m³) for each additional user.”
Two people: 18,000 litres. Four people: 18,000 + 6,800 + 6,800 = 31,600 litres.
The same document asks a septic tank serving four people to hold 2,700 litres. A cesspit for the same family must be nearly twelve times larger.
A septic tank only has to hold sewage long enough for the solids to settle. The liquid leaves continuously, and the ground does the actual treatment. So the tank only needs to be as big as a couple of days of flow.
A cesspit has nowhere to send anything. Every litre of water your household uses — every shower, every washing machine cycle, every flush — has to sit there until a tanker removes it. Eighteen thousand litres is not a treatment volume. It is a buffer sized so the lorry does not have to come every week.
Which means the capacity rule is really a warning label. The regulations are telling you, in the only language they have, that this thing will be emptied a great deal.
Nobody will tell you how often, because nobody knows
Here is a thing worth noticing: the regulations set a capacity but no emptying schedule. There is no legal frequency for a cesspit anywhere in the UK — unlike a septic tank in England, which the Environment Agency wants “emptied at least once a year”.
So the trade fills the silence, and it cannot agree with itself:
Emergency Repairs London: “Every 2–4 weeks if occupied”. FS Drainage: “every 4 to 8 weeks.” GRAF: “around every 45 days”. PumpRound: “typically needs emptying every 7–8 weeks”.
They are not lying to you. They genuinely cannot know, because the answer is a function of your household’s water use and nothing else. A cesspit is a bucket under a tap: how fast it fills depends entirely on how much you run the tap.
What it actually costs to own
MyJobQuote’s figure for emptying: “Cesspit emptying costs are usually between £175 and £300 per visit”.
Now combine the two things nobody puts side by side:
| Frequency (trade’s own figures) | Visits per year | At £175 | At £300 |
|---|---|---|---|
| Every 4 weeks | 13 | £2,275 | £3,900 |
| Every 6 weeks | 9 | £1,575 | £2,700 |
| Every 8 weeks | 6.5 | £1,138 | £1,950 |
Roughly £1,100 to £3,900 a year, forever, to own a hole in the ground that treats nothing.
Against that, the same country’s septic tank owners report figures like these — not from a price list, but from each other:
I've heard prices of £150-£200 locally to empty an average tank.
rich r, mig-welding.co.uk forumThat is a similar price per visit. The difference is that the septic tank owner might pay it once a year, and the cesspit owner pays it nine times.
So the arithmetic almost always says: get off the cesspit. The reason people do not is that the £20,000 is invisible — it leaves in £250 slices, nine times a year, each one too small to trigger a decision. The replacement is one visible cheque.
If you have a cesspit and the ground will take a drainage field, the only question worth asking is why you are still paying the instalments on a system you do not have.
Where it can go, and why access is the whole design
- The pipework. "Cesspools do not have an outlet pipe or drain." A septic tank has one, feeding a drainage field.
- The interval. A lorry every few weeks is a cesspit. A lorry once a year is a septic tank.
- The volume. 18,000 litres for two people means cesspit. 2,700 litres for four means septic tank. No overlap.
- The notice. The regulations require "a durable notice" in the building describing the maintenance. Ask the seller for it — the answer is informative either way.
Two siting rules from Approved Document H, and both are about the lorry:
“1.59 Cesspools should be sited at least 7m from any habitable parts of buildings and preferably downslope.”
“1.60 Cesspools should be sited within 30m of a vehicle access and at such levels that they can be emptied and cleaned without hazard to the building occupants or the contents being taken through a dwelling or place of work.”
Seven metres from the house is the smell-and-nuisance rule. Thirty metres from vehicle access is the one that matters more, because a cesspit is defined by the tanker: if a lorry cannot reach it, the system does not function at all. Not “functions worse” — does not function.
That last clause — the tank must be “emptied and cleaned without hazard to the building occupants or the contents being taken through a dwelling” — is the regulation’s polite way of saying that nobody should ever have to run a hose through your kitchen.
The rest of the design requirements are equally blunt about what a cesspit is:
“1.62 Cesspools should have no openings except for the inlet, access for emptying and ventilation.”
“1.63 Cesspools should prevent leakage of the contents and ingress of subsoil water and should be ventilated.”
That second one cuts both ways, and the second half is the one that ruins people. A cesspit must keep sewage in — obviously. It must also keep groundwater out. A cracked cesspit in wet ground fills with rain and water table, and you pay £250 a visit to have a tanker remove clean groundwater from your garden. It is the most expensive way to drain a field ever devised.
Factory-made cesspools, like septic tanks, sit under a product standard: “1.65 Factory-made cesspools are available in glass reinforced plastics, polyethylene or steel and should meet the relevant requirements of BS EN 12566-1.”
So when is a cesspit right?
When it is the only thing left. That is not rhetoric — it is what the decision tree actually looks like:
- Can you connect to a public sewer? Then do that. gov.uk expects it where reasonable.
- Will the ground take a drainage field? Run the percolation test. If your Vp lands between 12 and 100, a septic tank with a drainage field is legal, cheaper to buy and vastly cheaper to run.
- Is there a watercourse? Then a sewage treatment plant can discharge to it — a septic tank cannot.
- None of the above? Now, and only now, a cesspit.
That last case is real: impermeable clay, no watercourse, no sewer, a listed building with nowhere to put a field. In those spots a cesspit is not a bad choice, it is the only lawful one, and the £2,000 a year is the price of the plot’s geology.
What a cesspit is never is the cheap option. The tank is bigger, the hole is bigger, and then you pay for the rest of your life.
Look for an outlet pipe. "Cesspools do not have an outlet pipe or drain." If nothing leaves the tank, it is a cesspit.
Yes — the regulations require "a durable notice" fixed in the building describing the maintenance. Almost nobody has one.
Effectively. Every few weeks is storage. Once a year is treatment.
Frequently asked questions
What is the difference between a cesspit and a septic tank?
A septic tank treats: solids settle, bacteria digest, and the liquid leaves through a drainage field where the soil finishes the job. A cesspit does none of that — Approved Document H requires it to have “no openings except for the inlet, access for emptying and ventilation”. It is a sealed holding tank. Everything that goes in stays in until a tanker takes it away.
How big does a cesspit have to be?
Approved Document H §1.61: “Cesspools should have a capacity below the level of the inlet of at least 18,000 litres (18m³) for 2 users. This size should be increased by 6800 litres (6.8m³) for each additional user.” So two people need 18,000 litres, three need 24,800, four need 31,600. For comparison, the same document asks 2,700 litres of a septic tank serving up to four people.
How often does a cesspit need emptying?
There is no official frequency anywhere in the UK — the regulations set a capacity, not a schedule. The trade's estimates disagree wildly: Emergency Repairs London says “Every 2–4 weeks if occupied”, FS Drainage “every 4 to 8 weeks.”, GRAF “around every 45 days”, PumpRound “typically needs emptying every 7–8 weeks”. The honest answer is that it depends on how much water your household puts down the drain, and nobody can tell you without watching your tank.
How much does a cesspit cost to run?
MyJobQuote puts cesspit emptying at “usually between £175 and £300 per visit”. At the trade's own suggested frequencies — every four to eight weeks — that works out at roughly £1,100 to £3,900 a year. Over ten years that is the cost of replacing the system several times over.
Where can a cesspit legally go?
Approved Document H §1.59: “Cesspools should be sited at least 7m from any habitable parts of buildings and preferably downslope.” And §1.60: “within 30m of a vehicle access and at such levels that they can be emptied and cleaned without hazard to the building occupants”. A cesspit a tanker cannot reach is not a cesspit, it is a future emergency.
When is a cesspit the right choice?
When nothing else is legal. If your ground fails the percolation test — outside the Vp 12–100 band — you cannot have a drainage field. If there is no watercourse to discharge to and no public sewer to join, a sealed tank is what is left. It is a last resort by design, not a cheap option.
Researcher & editor, off-mains drainage
Writes independent guides on septic tanks, cesspits and sewage treatment plants for homes off the mains. Cross-checks the general binding rules and the Environment Agency, SEPA, NRW and NIEA against real prices, British Standards and what owners actually report on the forums.