Understanding Septic Tank Systems

Septic tank systems vary depending on their location, the waste volume generated, and how that waste is transported. Traditional systems rely on anaerobic bacteria to begin separating solids from liquids within the tank. From there, waste liquid flows into a drainage system - a network of perforated pipes laid in trenches - which allows the liquid to percolate through the surrounding soil. This process supports further treatment by filtering contaminants as the water moves through the ground.

In remote or inaccessible locations, larger drainage fields or pump-assisted systems are often required to manage outflows where gravity-fed designs are not practical. Sewage treatment plants offer an alternative, using oxygen and mechanical components to process waste on-site in line with environmental regulations.

In residential or built-up areas, smaller drainage fields may be shared between properties, or properties may be connected directly to the mains sewer network depending on local infrastructure.

What Are the Septic Tank Construction Rules?

Septic tank construction must be planned from the outset with environmental protection and public health in mind. The system must be designed and installed to prevent contamination of drinking water supplies and the surrounding environment.

Several legal frameworks apply, including the Environmental Permitting (England and Wales) Regulations 2016, the Environmental Protection Act 1990, and the Water Industry Act 1991. These set the standards for waste discharge, pollution control, and water resource protection.

In addition to permitting and compliance requirements, there are technical rules for tank design and siting that support these objectives. These include minimum distances from buildings and water sources, construction material specifications, and discharge conditions if your septic tank discharges directly into a watercourse. All of these contribute to safe, lawful, and effective operation.

Siting specifications

The placement of a septic tank with an off-mains drainage system must comply with Part H of the Building Regulations 2010 (Drainage and Waste Disposal) and General Binding Rules. These regulations set out requirements to protect public health and prevent environmental contamination. The following siting criteria should be observed:

• Minimum distance from buildings: The septic tank must be installed at least 7 metres from the habitable parts of any building. Wherever practical, the tank should be located on ground that is downslope from the building.
• Access for tanker vehicles: If the tank will require periodic emptying, access for a vacuum tanker must be planned in advance: The tank should be located within 30 m of a suitable vehicle access point. This distance applies only where the invert level of the tank (the depth from ground level to the base of the tank inlet) is no more than 3 metres below the vehicle access level. If the invert level exceeds 3 m, the height difference between the vehicle access point and the tank may need to be reduced to allow for safe and effective removal of wastewater.
• Unobstructed route for emptying: There must be a direct, unobstructed route to the septic tank for emptying and maintenance. The route must allow: Safe tanker access without the need to pass through any part of a dwelling or place of work. Adequate space for hose deployment, connection, and waste removal without risk to people or property.

Failure to meet these siting standards may affect system performance and increase the risk of environmental pollution or access restrictions during scheduled or emergency servicing.

Sewage tank construction

Septic tank installations must be designed and built to meet structural standards and regulatory requirements. The following specifications apply:

• Flow control: Tanks must be designed to minimise the flow rate of blackwater, allowing solids to settle effectively.
• Access for inspection: Inlet and outlet pipes must provide suitable access for sampling and inspection.
• Capacity requirements: The volume below the inlet level must be at least 2.7 m³ for up to four users. The size must be increased by 180 litres for each additional user.
• Standards compliance: All septic tanks must meet the specifications of BS EN 12566-1.
• Structural construction: Brick construction: walls must be at least 220 millimetres thick. Mortar: a 1:3 cement-to-sand ratio must be used. Concrete construction: walls must be a minimum of 150 mm thick.
• Watertightness and ventilation: Tanks must prevent leakage of waste and ingress of subsoil water. They must be ventilated, with vents positioned away from buildings.
• Internal design: Tanks must include at least two chambers or compartments at the inlet and outlet.

If the tank’s internal width is less than 1.2 m, the inlet must be fitted with a dip drainage pipe.

Ground conditions

The ground conditions must support effective percolation of sewage discharge throughout the year. Suitable subsoils include sand, gravel, chalk, sandy loam, and clay loam. These are typically well-drained and aerated soils, often identified by their brown, yellow, or red colouring.

Before construction begins, a preliminary assessment should be carried out in consultation with the Environment Agency and the local authority to confirm the suitability of the proposed site. A percolation test must also be completed - this should be conducted at least three times using a minimum of two separate boreholes to provide reliable data on infiltration capacity.

How Universal Tankers Can Help

Universal Tankers provides specialist wastewater removal services to support compliant, efficient on-site sewage system management. Whether you're working on a new septic tank build, infrastructure project, or ongoing development, our services are designed to reduce risk, prevent disruption, and keep your system operating at full capacity.

We help you stay compliant with all relevant legislation such as the General Binding Rules and Environmental Permitting (England and Wales) Regulations 2016. Our approach protects against pollution, enhances system efficiency and supports the longevity of your sewage infrastructure.

We offer:

• Guaranteed next-day service across England and Scotland. Wherever your site is located, our team will be there when you need us - even in hard-to-reach or remote areas.
• 20 strategically located depots across England and Scotland, allowing us to respond quickly to routine or emergency requirements with minimal downtime.
• Flexible service schedules, including one-off collections, emergency response, and regular weekly or monthly visits, tailored to your site activity and wastewater volumes.
• Capability to support any size of project, from a small sewage treatment plant within residential dwellings to large-scale commercial and infrastructure developments. We are a trusted partner to a wide range of sectors including construction, utilities, events, and agriculture.
• Accredited, compliant operations, with certifications including Achilles, SafeContractor, Constructionline Gold, and FORS - giving you full confidence in the quality, safety, and professionalism of our services.

All wastewater is collected and disposed of using approved processes in line with environmental regulations. Our team is experienced, highly trained, and committed to supporting your project without delays or disruption.

Whether you require planned support or urgent assistance, we work around your schedule to keep your site operational and compliant at all times.