Can you install an underground water tank by yourself?

Can you install an underground water tank by yourself?

June 24, 2018 0 By Saidul Hoque

An underground tank can be defined as any tanks and connecting piping that holds at least 10% of its combined volume below ground. People who purchase underground tanks are typically looking to maximise their available land use since the tanks can be installed under the compound. They also allow one to store large amounts of water.

Generally speaking, underground water tanks last longer than above ground water tanks. One particular reason for this is the fact that above ground water tanks are more prone to damage from environmental factors. As an extreme example, in the case of a hurricane, an above – ground tank will be damaged much more than an underground tank.

Because of these factors, many individuals may opt for an underground tank over an above – ground tank. However, installing an underground tank is decidedly more difficult than installing an above ground tank. In this article, we will assume that one wishes to install a standard fully underground poly tank. Before you attempt to install any tank, however, be sure to read all warnings provided on the tank lid before installation. The article will also provide best practice standards for preparation.

Generally, installing an underground tank involves the following steps:

  • Excavation
  • Base preparation
  • Setting the tank
  • Backfilling


Excavation is generally digging a large hole. Make sure to pick a good area for excavation, preferably one with adequate sub – soil drainage. Once this is done, take the measurements of the tank. Standard practice for such excavation includes adding about 18 inches on both ends and sides of the water tank, Dig the hole down to a depth that provides a minimum cover of about 6 inches over the top of the water tank. However, if available, excavate the hole in accordance with the drawings provided by the engineer.

underground water tank


Base Preparation

This generally involves removing any plant roots that may be in the way and flattening the base. Place screed as well as compact 50mm of metal dust in the base of the hole. Compaction itself should be achieved by using water and a vibrating plate. This ensures a firm flat surface for the water tank as well as ensuring that the tank is not damaged during its useful life.


Setting the Tank

Lift the water tank into the hole, carefully positioning it. Since you gave room for the tank on every side, you should try to install the water tank dead centre within the hole. Attach and add connections as instructed by the manufacturer. Now fill the tank with water. Ensure the riser, if required, and the manhole cover is fitted to make sure nothing can enter the tank during the installation process.  Afterwards, add another 50 mm of film material (metal dust) to ensure the cavities around the feet are filled and the tank is properly supported.

Place film material around the tank in 200mm stages and compact using water and a vibrating plate. As a precaution you could carefully move the tank back and forth to ensure it is firmly planted within the metal dust.

If the tank is positioned in a driveway leave the pier/peer cavities void. Otherwise, for a backyard installation, these piers also need to be filled and compacted. Connect all inlets, outlets,overflow plumbing, pump and electrical wiring before filling the tank piers with vibrated concrete.



If the installation is under a driveway or anywhere with traffic, pour, vibrate and finish the concrete to the engineer’s specifications. If the installation is in a yard situation, place 200mm of top soil and turf. Finally, complete all pump and controller wiring, install the first flush diverters, overflow flap valve and seal the manhole cover with the seal provided.

Your tank should now be ready for use. Make sure the diverter and any filters are regularly maintained over the life of the tank to extend the tank’s useful life.


Bottom Line

It is quite possible for you to install an underground tank by yourself but as illustrated, it is a considerably complex process; the process also allows very little room for error. For instance, if you begin filling the area around the tank before setting the base properly then it may be difficult to remove the filling just to fill it properly. Furthermore, you may even fill the base incorrectly or set the base unevenly. So, in as much as it is possible to carry out the entire process yourself, you may want to hire a professional team to conduct the entire process for yourself.


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