What are the installation requirements for a large underground tank?

It is essential you follow the manufacturer's instructions for fitting or the guarantee will be void. The installation instructions of a typical kit may be downloaded here b) If the ground where the tank is to be installed is well drained and has a low water table, back filling with sharp sand, earth or pebbles is OK. You are advised by the tank manufacturers to provide a concrete base of 150mm under the tank. c) If the ground is habitually wet or the water table is high, there must be a beam or concrete to prevent the tank when empty from popping up out of the ground. Yes, it happens. Alternatively, drain the area directly around the tank with a pump if needed. d) MDPE tanks are not normally strong enough to keep their shape in compression so the tank must be filled with water as you proceed with backfilling.  more