Septic tanks

How they work and the crucial maintenance tasks required.

Septic tanks hero

Many homes, especially those in rural areas, are not able to connect to a town sewage system. These properties have their own on-site disposal systems. The most common form of on-site disposal system is a septic tank.

How do they work?

Wastewater, from the kitchen, laundry and bathroom, discharges into a septic tank buried on the property. The heavier solids settle to the bottom of the tank, while fats float to the top. The remaining liquid flows out of the tank and discharges into a soakage area (either a dispersal or evaporation field).

Modern septic systems may have pumps, pressurized disposal with multiple chambers and filters. Speak to the manufacturer of your system to get an understanding of how your particular system works. The information given here applies mostly to older style systems.

Don’t go into a septic tank!

Your septic tank contains toxic gases that could kill you if you breathe them in. Never enter the septic tank yourself, and never leave the lid open.

Maintenance is crucial

A poorly maintained septic tank will become a serious health hazard, spreading disease and contaminating water sources. Septic tanks need regular maintenance, some of which you can do yourself and some of which you’ll need professional help with.

Learn about your particular system and keep a maintenance record. Include drawings of the system, mapping out its exact location. Your local council may be able to provide you with some of these details.

Newer systems often include a maintenance contract in their price. It is worth considering buying a maintenance contract for older systems.


Tanks generally need pumping (cleaning out) every 3-5 years to remove sludge and sediment.

The frequency depends on:

  • What goes into the system.
  • How many people use it.
  • The capacity of the tanks.
  • Whether you recycle greywater.

You’ll need a professional to do the pumping. Look under Septic Tanks, Water Treatment, or Water & Wastewater Services in the Yellow Pages.


Tanks need to be inspected regularly. You’ll need a professional to do this for you.

Look under Septic Tanks, Water Treatment, or Water & Wastewater Services in the Yellow Pages.

Protect the soakage treatment area

Protect the soakage treatment area so that the effluent leaving the tank has best conditions to disperse or evaporate. Don’t let vehicles onto the area, nor anything else that might break up the surface (such as animals or, in winter, children running around).

Don’t overload your tank

The best way to keep maintenance to a minimum is not to overload your tank with too much wastewater.

Most of your wastewater comes from your washing machine, toilet and bathroom.

Rubbish and toxins

What you put into your septic tank will determine how much maintenance it needs.

To keep it working effectively:

  • Don’t do multiple loads of laundry in one day.
  • Don’t empty large quantities of water into the system all at once, such as from a spa pool.
  • Don’t let rainwater into the septic tank.
  • Put only sewage and 2-ply toilet paper into the system – everything else should go in the bin, including nappies, tampons, plasters, dental floss and chemicals.


Blockages are usually a sign that the sewage disposal system either requires maintenance or repair. Blockages can be either between the house and septic tank or between the tank and the soakage area.

  • A blockage between the house and septic tank could be caused by the scum layer of the tank plugging the inlet pipe at the tank, or it may be a blocked gully trap. Try clearing the blockage with a rubber plunger or drainage rod. If this does not work you should contact a professional. If scum is blocking the inlet pipe it is likely that the tank needs to be pumped out by professionals.
  • A blockage between the septic tank and soakage area could be due to lack of maintenance and is likely to be caused by deterioration of the outlet baffle, particularly on an older system. You will need to have the tank pumped and the baffle replaced.
  • An obstructed line to the soakage area is probably due to either solids passing through the septic tank or broken pipes. Get the tank pumped out and have any broken pipes repaired.
  • A clogged soakage area can get happen naturally over time. If possible, rest the soakage area. This is possible with many modern systems that have two dispersal lines. However, switching lines should be done in summer when soil temperatures are high.
  • Seepage or swampy conditions in the soakage area can be due to the soakage area being too small or a clogged soakage area.

Older systems may have trouble coping with the amount of water modern living produces. This is particularly the case if you have extended your home and added bathrooms, for example, without expanding the on-site disposal system.

You can try to reduce the amount of water you are putting into the system. If this doesn’t solve the problem you may need to consider a larger system. Contact your local council for advice on this.

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