Invicta

Invicta tanks are typically sized by population equivalent, usually starting around 2,700 litres for a small household and scaling up from there. As a rule of thumb, Building Regulations require sizing for the number of bedrooms plus a margin, so a 4-bedroom house would normally need a larger tank than a 2-bedroom cottage. If you're unsure, check the manufacturer's sizing table against occupancy rather than just square footage.

Invicta tanks are manufactured from durable polyethylene, chosen for its strength, chemical resistance and lighter weight compared with GRP (fibreglass). Polyethylene tanks are generally easier to handle on site and less prone to cracking under ground movement, though correct backfill and installation are still essential to prevent flotation or deformation. Both materials perform well when installed to the manufacturer's specification, so the choice often comes down to site access and installer preference.

Most domestic septic tank installations fall under Building Regulations (specifically Part H) rather than requiring full planning permission, but you must notify your local authority via a building control application. If the tank discharges to a watercourse or is in a sensitive area, you'll also need to register the discharge with the Environment Agency or check whether a permit is required. Always confirm percolation test results before finalising your installation plan, as this affects both compliance and drainage field design.

Standard Invicta tanks are designed for installation in garden or non-trafficked ground; if the tank sits under a driveway or any area subject to vehicle loading, you'll need a traffic-rated cover and, in many cases, a reinforced surround or concrete slab to spread the load. Always check the specific model's loading rating before siting it under a drive, as not all tanks in the range are rated the same way. Getting this wrong risks structural damage to the tank and costly remedial work later.

Installation involves excavating to the correct depth, laying a stable base (typically pea shingle or as specified), lowering the tank in, and backfilling in stages while the tank is filled with water to prevent flotation and pressure damage. Correct pipework alignment to the inlet and outlet, along with ventilation, is critical for the system to function properly. We'd always recommend using a groundworker familiar with septic tank installation, as errors at this stage are the most common cause of future problems.

Larger Invicta tanks are usually delivered on a kerbside basis via HIAB or similar crane-equipped vehicle, so you'll need suitable access and a clear, firm area for the driver to offload safely. It's worth confirming ground conditions and access width in advance, particularly for rural sites with narrow lanes or soft verges. Delivery lead times can vary depending on tank size and stock levels, so it's best to check current availability before scheduling groundworks.