Burying a water tank is sometimes desirable to reduce their height, or placing them completely underground if you don’t have much surface space. Poly water tanks are the ideal solution, since steel tanks obviously can’t be buried since they will rust and corrode. This article will reveal what you need to know if you wish to fully or partially bury your poly tank.
Partially Burying a Poly Tank
Firstly, you shouldn’t just bury any poly tank since the strength of walls can vary greatly across different brands. If too thin, or not properly supported, then they can collapse inwards due to pressure outside the tank.
It is important to seek the advice of an engineer before proceeding – some councils require this when digging more than a metre below ground. Soil type, desired depth and location must be evaluated by an expert when partially burying your tank to ensure the foundations do not erode.
Again, it is important to emphasise that a wide range of poly tanks on the market are different from each other. Some have thicker walls, others have ribs, and it is important to consult your tank manufacturer before attempting to partially bury. While not ideal, you may partially bury National Poly Industries’ round poly tanks so long as you follow our “Site Preparation” instructions.
As a guide, we recommend burying your poly tank no more than 1 metre into the ground. It is important to dig your hole 300mm (12 inches) wider than the base diameter of your tank. If two tanks are to be buried side-by-side then separate holes must be dug.
Your tank foundations must be prepared as per normal. That is upon an appropriate level and flat concrete or crusher dust base. Once the tank is situated in the centre, fill your tank with water, then backfill the hole with compacted crusher dust (3 parts) and cement powder (1 part). Compact 75 to 100mm at a time. We also recommend erecting a fence around the tank for safety reasons.
Fully Burying Your Tank Underground
You should never completely bury a tank intended to be on the surface. While it isn’t appropriate to completely bury a regular surface tank, there are very strong purpose-build underground poly tanks on the market. An advantage of an underground poly tank is that they are a lot less expensive than concrete tanks, made to withstand external pressure and are easy to install.
National Poly Industries’ underground tanks require shallow excavation (between 1 to 1.3 metres), can be dug with a shovel on a weekend, and are available in different sizes of 1,500 litres, 3,000 litres and 5,000 litres. They are designed to provide a completely hidden water storage solution, and suitable for installation under a driveway, pathway or yard.