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Septic Tanks, Cess Pits and Biodiscs

Drains and Sewers

Septic tanks

Septic tanks are typically a two or three chamber system where sewage is retained to enable the settlement of solids, biological digestion and effluent discharge.

Effluent from a septic tank may be disposed of via a soak-away, provided that it does not present a pollution risk to ground or surface water. A percolation test will usually be required prior to tank installation (see point 3 on drainage fields below).

Things to consider:

Tank Capacity

The size of the tank must be suitable for the number of people or households that intend to use it. Your tank installer should be able to advise you on this.

Tank location

There are a few things to bear in mind when planning the location of your septic tank:

  • Tanks and soak-aways should ideally be located at least 15 metres from any dwelling.
  • Tanks and soak-aways should never be located near to a well or borehole.

Drainage Fields

It is important to find out at an early stage whether or not your ground conditions are suitable for the installation of a drainage field.

A simple percolation test will be conducted (your tank installer may be able to do this).

The area of your drainage field will also be determined by the number of people using the septic tank.

Generally a drainage field should not be sited closer than 10 metres to a ditch, drain or other watercourse. Soak-away pipes should be buried as shallow as possible (usually within 1 metre of the grounds surface).


Cesspools and Cesspits are covered watertight tanks that receive and store sewage. No treatment of the sewage occurs in the tank, and it will require frequent emptying.

Things to consider

  • They should be located no closer than 15m from your house.
  • The minimum capacity (from the Building Regulations) is 18 cubic metres or at least 45 days storage.
  • Rainwater should not collect.

Bio discs

Things to consider

  • Biodiscs may serve multiple properties and may be more appropriate than many septic tanks.
  • A constant supply of electricity is required to turn the biological filter
  • Consent from the Environment Agency is required to discharge to a watercourse.

The Law and Septic Tanks, Cesspools and Biodiscs

Septic tanks, cesspools and biodiscs are a very effective way to deal with sewage. However, those using them have responsibility for their maintenance and repair. It is an offence under the Public Health Act 1936 to allow septic tanks, cesspools and biodisc to leak (with the exception of treated effluent) or overflow and enforcement action can be taken by Environmental Health should this occur.

Permission may be required from Building Control

Tel: 01895 837296

email: buildingcontrol.csb@buckinghamshire.gov.uk