Septic tank systems

A septic tank system is a type of wastewater management system.

It is usually installed when a property is not connected to sewerage.

It is designed to separate solids, grease and oils from wastewater.

How a septic tank system works

A septic tank system works as follows:

  1. Wastewater passes through the septic tank.
  2. Heavier solids sink to the bottom.
  3. Bacteria breaks down the solids and changes it to sludge.
  4. The sludge builds up in the bottom of the septic tank.
  5. Grease and oil float to the surface to form a crust over the liquid (scum).
  6. The remaining liquid (effluent) flows from the tank into the drainage beds or trenches.
  7. The liquid soaks into the surrounding soil.

How to look after your septic tank system

If you own a septic tank system, you are responsible for making sure it works properly.

Find out how to maintain and pump out your septic tank system.

You should also check your septic tank after a flood or cyclone.

Remove, reuse or destroy a system

If you no longer need your septic tank, find out how to remove, reuse or destroy it.


Ballina Shire Council, NSW (2017) fact sheet 2 - How your septic tank works, BSC website, accessed November 2020.

Last updated: 02 December 2020

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