Installation at a Glance

Before installation

• Confirm the tank delivered is the correct capacity, dimensions and configuration for the project.
• Check the connection orientations, filter requirements and any associated invert-level changes.
• Confirm site access, delivery arrangements and suitable equipment for unloading.
• Check ground conditions, soil type, water table, excavation depth, nearby foundations, utilities, slopes/banks and trees.
• Complete the required risk assessment and method statement (RAMS).
• Check the installation does not fall outside the standard installation conditions. Structural engineering advice is required where:
  • Vehicles other than ride-on lawnmowers will traffic over the tank.
  • The tank is within 4 m of another structure’s foundations.
  • The tank is within 4 m of a significant change in ground level.
  • The installation is outside the specified depth parameters.
  • Heavy clay or high water-table conditions are present.

Delivery & handling

• Inspect the tank before unloading and check it against the delivery documentation.
• Make sure suitable plant, access and a clear route to the installation location are available.
• The tank must only be lifted and manoeuvred when empty.
• Never lift the tank when it contains water.
• Use the designated lifting points with suitable lifting straps/chains and appropriately sized D-shackles.
• Establish the tank’s centre of gravity before fully raising it and use guide ropes to control movement from a safe distance.

Excavation & base

• Calculate the excavation depth from the drainage design and confirm the minimum and maximum permitted cover will not be exceeded.
• Allow sufficient room for tank manoeuvring and access, plus any battering required for the ground conditions.
• Allow for possible groundwater ingress during excavation.
• If the ground needs stabilising, the guide specifies increasing excavation depth by 250 mm and replacing it with a mixture of hardcore and sand.
• Provide a 50 mm bed of 10 mm washed pea gravel at the bottom of the excavation.

Positioning the tank

• Position the tank on the pea-gravel base and check both horizontal and vertical alignment.
• Allow for approximately 10 mm of settlement.
• The service duct must align with the controls inside the building because the supply pipe has limited flexibility.
• On direct-pressure systems, the service duct must slope towards the tank to allow gravity-fed mains-water top-up.
• Be aware of filter invert drops:
  • PF filter: 66 mm
  • VF-1 filter: 300 mm

Pipework

• Minimum pipe fall is 1:100 in the direction of water flow.
• Rainwater inlet pipework and service duct should fall towards the tank.
• The overflow should fall away from the tank.
• Connect the rainwater inlet, overflow and service duct once the tank has settled into position.
• Keep all rainwater-harvesting pipework free from site debris and seal pipe ends during construction.
• Make sure the overflow is connected to the appropriate surface-water management system.

Backfilling

• Initially fill the tank to one-third full with water to settle it into the pea gravel.
• Make final alignment adjustments to the connections and pipework.
• Install the neck and seal the joints with a good bead of silicone sealant to prevent groundwater ingress.
• Backfill around and beneath the tank using 10 mm washed pea gravel.
• Keep the pea-gravel backfill level in line with the water level inside the tank.
• Continue until the tank crown has 50 mm of pea-gravel cover.
• Continue filling the tank with water as backfilling progresses, up to the level of the inlet/outlet connections.
• Complete the remaining backfill to finished ground level using free-flowing material.

Finishing & commissioning

• Secure the tank lid.
• Install the filter if it has not already been fitted.
• Cover the filter with strong polythene to prevent roof water entering the tank before the system is ready for use.
• Remove the protective filter covering during commissioning.
• Clearly mark the tank location.
• Establish a 4 m exclusion zone outside the original excavation footprint to prevent construction vehicles accidentally driving over the tank.