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Last edited 16 Apr 2021
A cesspool is an underground tank used to collect wastewater and sewage. It will typically have a manhole for access, but does not have an outlet and does not discharge any of its contents. Unlike a septic tank, a cesspool does not process or treat wastewater and sewage it simply stores it.
Cesspools are sometimes referred to as cesspits, although both terms can also be used to refer to a underground chamber that is not sealed at the bottom so as to allow liquid to seep into the surrounding ground (commonly referred to as a soak pit). This has not been permitted since the introduction of the Public Health Act 1936.
Cesspools should be inspected fortnightly and the level checked (an automatic alarm may be installed). The contents of the cesspool must be removed regularly (typically every month depending on size and usage – much more frequently than an equivalent septic tank) by a licensed waste handler using a vacuum tanker. This can be a significant expense.
Cesspools are generally only installed at properties that are not connected to the public sewer network and that do not have suitable ground to provide a septic drain field (required for the installation of a septic tank), or at locations such as campsites where chemical toilets are emptied that might prevent a septic tank from functioning correctly.
Permits are not required for cesspools, and they do not have to comply with the general binding rules that apply to septic tanks. However, planning permission and building regulations approval is needed to install a cesspool.
Requirements for the design, construction and maintenance of cesspools are set out in Approved Document H of the building regulations, which permits cesspools were the installation of a septic tank is not reasonably practicable.
Cesspools should be at least 7m from habitable parts of a building, preferably downslope, and must be adequately ventilated. They should be within 30m of vehiclular access. They should have a capacity of at least 18,000 litres for two users and a further 6,800 litres for each additional user. A filling rate of 150 litres per person per day is assumed when estimating filling rates.
Cesspools are generally manufactured from glass reinforced plastic, polyethylene or steel, or constructed from brickwork or concrete. Older cesspools of masonry construction may have deteriorated over time, resulting in leaks or weaknesses that can lead to collapse. Cesspools should be inspected periodically by a suitably qualified engineer to ensure they remain sound.
If a cesspool does not fill as quickly as expected, or if the level suddenly drops, it should be inspected for possible leaks. Allowing a cesspool to overflow or leak is an offence under the Public Health Act 1936, and allowing a cesspool to pollute a watercourse is an offence under the Water Recourses Act 1991.
 Related articles on Designing Buildings Wiki
- Air admittance valve.
- Approved Document H.
- Difference between drains and sewers.
- Drainage stack.
- Grease management.
- Miasma theory.
- Private sewer.
- Public sewer.
- Safe working in drains and sewers.
- Sanitary pipework.
- Section 102 existing sewer adoption.
- Section 104 new sewer adoption.
- Septic tank
- Soil vent pipe.
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