Check your septic tank after a flood or cyclone

If you have a septic tank system on your property, you should check it for damage after a cyclone or flood.

Most systems shouldn’t be affected as they are below ground.

However, flooding can cause damage if it enters the system.

How floodwater enters a septic tank

Floodwater can enter the septic tank system through:

  • the toilet
  • other fixtures or
  • the overflow relief gully grate.

How floodwater can affect a septic tank

If the septic tank is flooded, it can wash out solids and cause blockages or system damage.

Tanks, leach drains, pump pits and irrigation pipework can also fill with silt and debris.

This can reduce the capacity or effectiveness of the system.

How to check your septic tank for damage or failure

There are ways to check if your septic tank is damaged or not working properly.

Signs of damage

You should check your septic tank for the following signs of damage:

  • open covers or pits
  • ruptured or leaking systems (including pipes)
  • damaged or exposed pipes that may need capping or sealing off.

Signs of system failure

Signs of a failed system include:

  • a strong odour around the tank and land application area
  • blocked fixtures, with wastewater overflowing from the relief point
  • high sludge levels within the primary tank
  • sewage flowing up through the toilet and sinks.

If your system has been under floodwater

Don’t use anything that is connected to the system until all parts have been inspected and repaired.

That includes:

  • toilets
  • laundry
  • kitchen
  • bathroom.

Repairing your septic tank system

If you need to repair your system, you must contact a licensed plumber and drainer.

To find a licensed plumber and drainer, go to the Plumbers and Drainers Licensing Board website.

Your system should be pumped out by a listed waste contractor as soon as possible after the flood.

However, the water level in the ground surrounding the tanks must be as low as possible before you start.

Find a listed waste contractor on the Northern Territory Environment Protection Authority website.

Secondary treatment systems

Secondary treatment systems (STS) should not be used if it has been inundated with floodwater.

Isolate the electrical connection and call the service technician immediately.

Sewage overflows

If your property needs a sewage overflow clean-up procedure, you should wear personal protective clothing such as:

  • rubber boots
  • rubber gloves
  • washable or disposable overalls.

Everyone else should avoid the affected area until it has been thoroughly cleaned and disinfected.

You should also follow these safety precautions:

  • Assume anything touched by wastewater is contaminated.
  • Wash your hands and affected areas of the body thoroughly with clean warm water and soap, especially before eating or smoking.
  • Immediately wash and disinfect any wounds that come into contact with wastewater.
  • Change out of dirty clothes and wash clothes separately.
  • Clean and dry dirty footwear.
  • Contact your doctor immediately if you experience any illness.


For more information, email

Last updated: 30 November 2020

Give feedback about this page.

Share this page:

URL copied!