A septic tank is an underground settlement chamber that separates solid waste from liquid effluent. Solids settle to the bottom of the tank and are broken down by anaerobic bacteria, while partially treated liquid flows out to a drainage field (soakaway) for final treatment in the soil. Septic tanks are suitable for properties on permeable ground with sufficient space for a compliant drainage field.

Since January 2020, septic tanks in England are no longer permitted to discharge directly to a watercourse. If your existing tank discharges to a stream, ditch, or river, it must be replaced with a sewage treatment plant or upgraded with a compliant drainage field. DrainsCo advises on the most cost-effective route to compliance.

A sewage treatment plant (also called a package treatment plant) provides a higher level of effluent treatment than a septic tank. These systems use aeration and biological processes to produce a final effluent clean enough to discharge directly to a watercourse under the Environment Agency’s General Binding Rules — without requiring a drainage field.

DrainsCo installs treatment plants from leading manufacturers. Treatment plants are the recommended solution for properties with impermeable ground, limited space, high water tables, or where a drainage field is not viable.

A cesspit is a sealed, watertight tank with no outlet. All waste is stored and must be emptied regularly by a licensed tanker. Cesspits are a last-resort solution where neither a septic tank nor a treatment plant is feasible due to ground or space constraints. DrainsCo installs cesspits to the required standards but will always explore alternatives first due to the ongoing operational costs.

Most septic tank installations require a drainage field (also known as a soakaway or infiltration system) to disperse treated effluent into the ground. DrainsCo carries out percolation testing to assess your soil’s absorption rate, designs the drainage field to BS 6297 standards, and installs the full system with inspection access points for future maintenance.

Off-mains drainage in England is governed by a combination of Environment Agency General Binding Rules, Building Regulations Approved Document H, and the Environmental Permitting Regulations. DrainsCo designs every installation to satisfy all applicable requirements:

• General Binding Rules (2015, amended 2020) — These set the conditions under which a septic tank or treatment plant can operate without a bespoke Environment Agency permit. Key requirements include: no discharge to a watercourse from a septic tank, maximum daily discharge volumes, minimum distances from watercourses and water supplies, and system sizing for the property.
• Building Regulations Part H — All new off-mains drainage installations must meet Building Regulations standards for tank sizing, drainage field design, depth, access, and ventilation.
• BS 6297 — The British Standard for the design and installation of drainage fields serving septic tanks.
• Environmental Permitting — If your installation falls outside the scope of the General Binding Rules (e.g., daily discharge exceeds limits, or the property is in a sensitive area), a bespoke permit from the Environment Agency is required. DrainsCo manages the application process.