Check and pump out your septic tank

If you have a septic tank on your property, you are responsible for checking and emptying it.

This is also known as desludging.

Over time, sludge and scum (septage) build up and need to be removed for it to work properly.

You should seek advice from a licensed plumber and drainer about whether your septic tank needs to be desludged.

Always use a licensed waste handler to desludge your septic tank.

How sludge and scum build up

A layer of sludge forms when organic matter from the wastewater settles to the bottom of the tank.

This layer contains micro-organisms that digest the organic matter and reduce the amount of sludge.

Scum forms as fats, oils, grease and other light material float on top of the clarified liquid that has separated from the solids.

When the clarified liquid flows out of the septic tank, it is called ‘primary treated effluent’.

When to desludge your septic tank

A well-maintained septic tank only needs to be desludged once every 3 to 7 years.

This depends on:

  • whether the tank is big enough for the daily wastewater flow
  • types of personal care products used by household members
  • how much organic matter, fat, oil and grease wash down the sinks
  • the use of harsh chemicals such as degreasers
  • the overuse of disinfectants and bleaches
  • the use of antibiotics and other drugs
  • whether any plastic or other non-organic items are flushed into the tank.

After desludging

After desludging, tanks must not be washed out or disinfected.

They should be refilled with water to reduce odours and maintain plumbing fixtures.

A small residue of sludge will always remain in the tank. This is necessary to encourage bacterial action to begin again.

You should keep a record of your septic tank pump-outs.

Septic tanks and grease traps in remote communities

Septic tanks and grease traps in remote communities are usually desludged by a licensed waste handler contracted by:

  • regional councils
  • the Department of Housing
  • property owners
  • business proprietors.

Some remote communities have pump-out trailers to pump out their own septic tanks.

Signs your septic tank is not working properly

You should check for signs that your septic tank is not working properly.

Some of these signs include:

  • the sewage in the toilet or liquid waste from other fixtures flows away very slowly
  • liquid waste overflows
  • wet areas are seen at the top of the septic tank
  • foul smells from the septic tank or land application area
  • the grass around the tank is green and growing well.

If your septic tank shows any of these signs, it may need to be pumped out.


To find a list of certified plumbers in the Northern Territory (NT), go to the Building Practitioners Board website.

To find a list of licensed waste handlers in the NT, go to the NT Environment Protection Authority website.

Last updated: 01 December 2020

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