Cesspool Size & Emptying Calculator
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Cesspool Size & Emptying Calculator
Size a cesspool (a sealed holding tank with no outlet) from the number of users or bedrooms, then estimate how often it needs emptying and the likely annual cost. Built on UK Building Regulations (Approved Document H2, paras 1.61 and A.20–A.22).
Minimum cesspool capacity
Approved Document H2 (1.61): at least 18,000 litres (18 m³) for 2 users, increased by 6,800 litres (6.8 m³) for each additional user.
Emptying frequency & annual cost
A cesspool has no discharge, so everything must be tankered away. Emptying interval is estimated from a fill rate of 150 litres per person per day (AD H A.22).
Reference & rules
The sizing basis and the key facts about cesspools as an off-mains foul solution.
| Users | Min. capacity | Daily inflow | Days to fill |
|---|
Sizing. 18,000 L (18 m³) for 2 users, +6,800 L (6.8 m³) per additional user. Capacity is measured below the inlet level. The increment equals roughly 45 days’ storage per person.
Emptying. Inspect fortnightly for overflow; in practice cesspools are typically emptied monthly by a licensed contractor (AD H A.20–A.21). Fill rate for estimating is 150 litres per person per day. If the tank does not fill within the estimated period, check it for leakage.
When a cesspool is used. A cesspool has no outlet and provides no treatment, so running costs are high. It is normally a last resort — only where a septic tank or packaged treatment plant with a drainage field or watercourse discharge is not reasonably practicable. Building regulations require at least 45 days’ storage. Overflowing a cesspool is an offence.
This cesspool size calculator sizes a cesspool — a sealed holding tank with no outlet — from the number of users or bedrooms, then estimates how often it needs emptying and the likely annual cost. It follows Approved Document H2 (paragraphs 1.61 and A.20 to A.22). For the rules on private foul drainage, see the Environment Agency's general binding rules.
Minimum cesspool capacity
Approved Document H2 requires at least 18,000 litres (18 m3) for two users, increased by 6,800 litres for each additional user. Enter the population, or estimate it from bedrooms, and the calculator returns the minimum capacity. Because a cesspool only stores — it does not treat or discharge — it is large and is normally a last resort where a septic tank and drainage field are not possible.
Emptying frequency and cost
Everything that goes in has to be tankered away. From a fill rate of 150 litres per person per day, the calculator estimates the emptying interval for your installed capacity and the likely annual cost, which is the figure that usually makes people check whether a treatment plant would be cheaper to run.
Cesspool, septic tank or treatment plant?
A cesspool stores; a septic tank settles and discharges to a drainage field; a treatment plant cleans the effluent enough to discharge to a watercourse. If the ground can take it, a septic tank with a drainage field is usually far cheaper to run than emptying a cesspool.
Further reading: general binding rules for small sewage discharges · do you need infiltration testing? · gov.uk general binding rules.
Frequently asked questions
At least 18,000 litres for two people, plus 6,800 litres per extra person, under Approved Document H2. The calculator confirms the size from your population.
It depends on capacity and use. At 150 litres per person per day the calculator estimates the interval — often every few weeks for a family, which is why running costs are high.
The terms are used interchangeably for a sealed holding tank with no outlet. It is different from a septic tank, which discharges to a drainage field.
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