Domestic Private Drainage

Domestic Private Drainage

The majority of properties in the UK are connected to public main sewers. These connect to sewage treatment works where the effluent is processed.

Properties that cannot be connected to mains are mainly in rural areas and require what is generally referred to as ‘private drainage’ or ‘off-grid drainage’ to store or process their sewage.

Types of Private Drainage

Typically, there are 3 types of domestic private drainage:

  1. Cesspools
  2. Septic Tanks
  3. Package Sewage Treatment Plants

If you have a property with private drainage, you are responsible for maintaining the system. Failure to regularly maintain, service and de-sludge the tank may mean that untreated or insufficiently treated effluent being discharged into the surrounding area. This may result in prosecution and fines from the Environment Agency.

A private drainage treatment system should work effectively if maintained correctly.

More about the types of private drainage systems

A sewage treatment plant acts similarly to a septic tank, using the first two chambers to settle out the solid matter. Settled liquids will then discharge into the’ biozone’ chamber where the liquids are mechanically aerated and then further broken down by aerobic digestion. Fine solids will settle out in a final settlement chamber before discharge. Generally, a high-quality final effluent is achieved in accordance with EA regulations.

Desludging and routine maintenance of the plant is essential to ensure the system meets it consent to discharge. The frequency is generally determined by the manufacturer. As a rule, this is normally every 6-12 months.

To check if your treatment plant is meeting the required standard – call The Tank Sampling Company for a free quotation.

A septic tank is also an underground tank that uses a simple process to crudely treat the waste and then will discharge the settled liquids into a drainage field or soakaway.

As waste enters the tank, solids will either settle to the bottom of the primary chamber or form a crust on the surface. Settled liquors will pass through to a secondary chamber where further settlement will occur. Eventually the settled liquids will discharge under gravity to the soakaway.

The sludge that settles to the bottom of the tank will need to be removed regularly, generally every 6-12 months.

Care should be taken when using a septic system. Excessive use of cleaning products or discharging fats, oils and grease (FOG) can affect the bacteria contained in the system. Bacteria is vital to the biological processes that break down the waste.

A cesspool is effectively a sealed tank, normally underground, in which the effluent is stored. There is no treatment of the contents of the tank. Emptying is required frequently, generally monthly.

Cesspools are uncommon nowadays as they tend to be expensive to maintain due to the frequency of emptying. Cesspools are installed only where there is no other feasible alternative.

The 2020 Guidelines

Under the new guidelines, effective from 1 January 2020, septic tanks will be prohibited from discharging directly to a watercourse (a river, stream, ditch, canal, or surface water drain).

If this is the case with your septic tank, there are really only 2 options available to you.

  1. Reroute your discharge away from the watercourse and to a soakaway facility
  2. Replace the septic tank with a small package sewage treatment plant so the final effluent meets the required standard to enter a watercourse.

Urgent action is needed to meet the deadline.

Link to 2020 guidelines: General binding rules: small sewage discharge to a surface water – GOV.UK (

Sampling and Testing

Sampling and Testing of the final effluent from a sewage treatment plant or a septic tank can determine whether the drainage system is working as designed. A well performing plant will reduce pollution and should ensure that enforcement action by the EA of the local water authority does not happen.

For more information, please contact us..