Underground Water Tanks

Polymaster’s underground water storage tanks have a 15-year design service life and a 10-year manufacturer’s warranty when installed.

No, use purpose-built underground models engineered for soil/traffic loads. Slimline tanks aren’t designed for burial. Polymaster provides dedicated underground SKUs and installation specs for this use.

Install a submersible pump (Polymaster kits include options) and, if desired, an automatic mains changeover for easy supply to the home or garden.

• Step 1. Trench excavation: Excavate to spec with ~300 mm working clearance, safe battering, and a firm, level, compacted crushed-rock base.
• Step 2. Placement of tank: Lower via lifting lugs, set on the base, and level in both directions with feet stable.
• Step 3. Placing water in tank: Pre-fill to the specified volume to stabilise the tank and counter buoyancy if groundwater is below the midline.
• Step 4. Backfilling: Backfill evenly in ≤300 mm layers with 7 mm minus/type b crushed rock, hand-compact without stressing the tank.
• Step 5. Plumbing of feed and overflow pipes: Install the inlet and overflow with ≥1% fall; connect the overflow to the stormwater with an accessible non-return valve.
• Step 6. Mounting of the self-cleaning vortex filter urvf01: Mount vertically with adequate fall near the downpipe or beside the tank; connect per spec.
• Step 7. Plumbing up the submersible pump: Fit supplied pump fittings and lifting chain, connect discharge to outlet, and any mains changeover device.
• Step 8. Wiring the pump and pressure switch: Mount the controller/pressure switch, run cable in conduit, and have a licensed electrician complete wiring.
• Step 9. Inspection and servicing: Inspect and pressure-test for leaks; schedule periodic cleaning and function checks of filters and internal parts.
• Step 10. Landscaping and commissioning: Cover and finish with paving/landscaping; ensure the lid is sealed and commission the system.

The underground rainwater tank system must be installed by a qualified plumber/installer. Installation by a non-licensed person may void the warranty. All wiring must be performed by a licensed electrician. Follow the Polmaster underground water tank installation guide to ensure you have a successful installation.

Do periodic checks via the access riser: clear leaf traps/filters, flush sediment if present, and follow Polymaster’s installation & maintenance guidance (use licensed trades for confined-space work). This keeps water quality and system efficiency high.

Underground poly tanks store rainwater in a buried tank fed by an inlet from your roof. Water is delivered to your taps or garden either by gravity or a submersible electric pump with optional mains changeover. The setup includes a distribution outlet, an overflow to stormwater to prevent flooding, and an access riser/drain for inspection and cleaning (often with a vent and level gauge). Being underground keeps water cool and protected, reduces visual impact, and frees up usable yard or driveway space.