Correct tank base preparation is essential for the long-term performance of your Clark Tanks water tank. All tanks must be installed on a stable, flat and level base that provides continuous support across the entire underside of the tank.
Before delivery, please ensure your tank base has been fully prepared in accordance with the manufacturer’s requirements outlined below. Incorrect installation or inadequate base preparation may affect your tank’s structural integrity and manufacturer warranty.
Tank Base Preparation Requirements
Regardless of the type of base selected, the following requirements apply:
- The base must be flat, level, stable and properly compacted.
- The entire underside of the tank must be fully supported at all times.
- The base must be free from rocks, tree roots, sharp objects and uneven surfaces.
- The base must be sufficiently large to support the tank and provide the required surrounding clearance.
- The base must be protected against erosion, subsidence and undermining from water runoff.
- A minimum clearance of 150mm from fixed objects must be maintained to allow the tank to expand and contract naturally.
Minimum Tank Base Dimensions
Clark Tanks specifies the following minimum base dimensions in its Delivery & Installation Guide:
| Tank Type | Minimum Base Dimensions |
|---|---|
| Slimline Tanks | 100mm wider than the tank width |
| Round Tanks | 300mm greater than the tank diameter |
For example, a slimline tank measuring 1,080mm wide requires a base at least 1,180mm wide. A round tank measuring 3,690mm in diameter requires a base at least 3,990mm in diameter.
Suitable Tank Base Types
1. Compacted Crusher Dust Base
A properly contained and compacted crusher dust base is suitable for many Clark Tanks water tanks.
Crusher dust must be granular, with a particle size of less than 5mm, and contained within suitable retaining borders to prevent erosion or movement of the material.
Preparation instructions:
- Excavate at least 100mm of natural ground, ensuring the area is flat, level and free from rocks, roots and other obstructions.
- Construct a retaining border, such as garden sleepers, to contain the crusher dust and protect against erosion.
- Fill the retained area with at least 75mm of crusher dust. Dry cement powder may also be mixed into the crusher dust if desired.
- Thoroughly compact the crusher dust using suitable mechanical compacting equipment.
- Screed the finished surface until it is completely flat and level, with no high or low spots.
Important: Sand is not an acceptable tank base material. Crusher dust must be properly contained and compacted before delivery.
2. Concrete Slab Base
A reinforced concrete slab is another suitable option for supporting Clark Tanks water tanks. The slab must be level, with no high or low spots, and finished with a smooth trowelled surface.
Clark Tanks specifies different concrete requirements depending on the tank type and capacity.
| Tank Type | Concrete Requirements |
|---|---|
| Slimline Tanks and Round Tanks under 40,000L | – Minimum 25MPa concrete – Minimum 100mm thickness – F62 reinforcing mesh positioned halfway through the slab |
| Round Tanks over 40,000L and Industrial Tanks | – 32MPa concrete – Minimum 150mm thickness – Two layers of F82 reinforcing mesh, spaced 75mm apart – 200mm wide × 200mm deep perimeter thickening with Y16 reinforcing bar at the bottom |
For large-capacity or industrial installations, professional advice should be obtained to ensure the slab and supporting ground are suitable for the weight and intended application of the tank.
3. Tank Stands
Clark Tanks water tanks may also be installed on a suitably constructed tank stand, provided the structure is designed to safely support the weight of the tank when completely full.
Clark Tanks recommends a flat, level hardwood timber decking surface, subject to the following requirements:
- Decking boards must have gaps no greater than 10mm.
- Supporting bearers must be sufficiently strong to prevent decking from sagging or deflecting under the weight of the filled tank.
- The tank must be lifted into position using a crane, with crane hire arranged at the customer’s expense.
- The tank must be securely fastened to the stand after positioning.
- All inlet and outlet pipework must be supported by the stand, not the tank itself.
- Flexible plumbing connections must be provided to accommodate movement without placing strain on the tank fittings or walls.
Tank stands should be appropriately designed and assessed for the intended load and installation conditions.
Plumbing & Installation Requirements
Polyethylene tanks naturally expand and contract as water levels and temperatures change. Plumbing connections must accommodate this movement without placing excessive pressure on the tank walls or fittings.
Outlet Connections
- Each water outlet must have a 300mm flexible hose installed between the ball valve and the adjoining plumbing.
- Rigid poly pipe is not considered a suitable substitute for this flexible hose.
- All connected pipework must be properly supported to prevent the weight of the plumbing from placing strain on the outlet fitting or tank wall.
- Where stub flanges are used, a suitable bellows or expansion joint must be installed.
Inlets & Overflows
- Overflow capacity must be sufficient to accommodate the volume of water entering the tank.
- For example, two 90mm inlet pipes require two 90mm overflow pipes or an equivalent overflow capacity.
- Overflow pipes must direct water away from the tank base to prevent erosion and undermining.
- When using charged downpipe systems, the pipework must be positioned at least 150mm away from the tank wall to allow for natural expansion and contraction.
- Fixed inlet pipes must be properly supported and fitted with flexible connections where required.
Unsuitable Tank Bases & Installations
Clark Tanks identifies several common installation mistakes that can damage water tanks and compromise their manufacturer warranty.
Avoid the following:
- Rocky or uneven ground: Sharp objects and uneven surfaces may damage the tank base or create concentrated stress points.
- Undersized tank bases: The full underside of the tank must be supported, with no portion extending beyond the prepared surface.
- Corrugated iron, bricks or unsupported timber sleepers: These must not be used as the tank’s supporting surface because they can shift, deform or place uneven pressure on the tank.
- Inadequate overflow drainage: Water discharged too close to the tank can wash away the supporting material and undermine the base.
- Unsupported plumbing: Rigid or unsupported pipes can place excessive strain on the outlet fitting and tank wall.
Retaining sleepers used around the outside of a properly prepared crusher dust base are acceptable; they must not be used as individual supports directly beneath the tank.
Immediately After Delivery
Once delivered, the tank must be secured against movement or wind damage. Clark Tanks requires either:
- at least 2.5cm of water to be placed into the tank; or
- the empty tank to be securely tied down.
The tank must be properly positioned on its prepared base, and any required installation work completed as soon as practicable.
Ongoing Tank Base Maintenance
Tank base maintenance remains important after installation. Clark Tanks recommends regularly inspecting the supporting surface and surrounding area for signs of:
- Erosion or movement of crusher dust and other base materials.
- Ground subsidence or sinking beneath the tank.
- Animal burrowing beneath or around the tank base.
- Water pooling or overflowing near the base.
- Plumbing connections placing excessive strain on tank fittings.
Tank inlet and overflow strainers should also be checked regularly and cleared of leaves, debris and other obstructions.
Please note: These requirements summarise Clark Tanks’ manufacturer installation instructions. Customers should refer to the full Clark Tanks Delivery & Installation Guide and obtain appropriate professional advice where necessary. Incorrect installation or maintenance can affect manufacturer warranty coverage. Your rights under the Australian Consumer Law remain applicable.