Water use, sustainability, and efficiency by choosing quality systems and materials, and providing environmentally friendly solutions.

Maintenance and problems

Owners are legally responsible for maintaining their on-site wastewater treatment system.

On this page:

  • Maintaining septic tank systems
  • Maintaining aerated water/advanced sewage treatment system
  • Maintaining land-application/disposal systems
  • Avoiding problems
  • Signs of trouble
  • Solving problems

Maintaining septic tank systems

  • Inspect tank annually for sludge and scum levels.
  • The tank should be pumped out approximately every 3–5 years. Have tank pumped out when:
    • the top of the floating scum is 75 mm or less from the bottom of the outlet
    • sludge has built up to within 250 mm of the bottom of the outlet
  • Check and clean outlet filters regularly (6-monthly)
  • Alternate dispersal to the land-application areas approximately every 3–6 months.

Maintaining aerated water/advanced sewage treatment system

AWTS and ASTS should be serviced by a qualified service person, generally every 6 months, to:

  • clean or replace filters as required
  • monitor the effluent quality, including pH level, of the first chamber
  • check the submersible pump and float switch operation
  • record all inspection maintenance and monitoring events
  • replace the submersible pump at 7–10 yearly intervals.

Maintaining land-application/disposal systems

  • Keep the area clear of deep rooting trees and shrubs (these may grow into and cause blockage of the system).
  • Clean and service pumps, siphons and filters according to manufacturers’ instructions.
  • Flush drip lines regularly to remove accumulated sediment.
  • Redirect effluent periodically to alternative trenches or beds (septic tanks).
  • Mow grass and maintain plants in evapo-transpiration areas.
  • Ensure that surface water drains around land-application areas are kept clear to reduce rainwater runoff into trenches or beds.

Avoiding problems

  • Specify water-efficient appliances to reduce the volume of wastewater going into the system.
  • Prevent overloading the system by minimising water use (e.g. spread heavy water-use activities such as clothes washing over several days) and installing a separate greywater treatment system.
  • Strong chemicals restrict the biological action within the tank – select cleaners and washing products that do not hamper the decomposition process, and make sure chemical products such as volatile thinners, bleaches and disinfectants do not enter the system
  • Kitchen waste should not enter on-site wastewater treatment systems – compost kitchen waste instead of installing a garbage disposal unit.
  • Systems cannot deal with condoms, dental floss, tampons, sanitary napkins, nappies and nappy wipes – these should be wrapped up and disposed of in the rubbish.

Signs of trouble

The system is not working correctly if:

  • there is a foul smell around tank or land application area
  • the tank overflows
  • the ground around the tank is soggy
  • sinks/basins/toilets are emptying slowly
  • fixtures make a gurgling noise when emptying
  • the grass is unusually dark green over the land application area
  • black liquid is oozing from the trenches
  • a gully trap or tank mushroom is overflowing.

Solving problems



Tank is too full

Have it pumped out

Tank contains too much sludge and scum

Have it pumped out/desludged

Too much water going into the tank

Use less water and check for stormwater infiltration

Toxic chemicals are going into the system

Reduce use of hard detergents/cleaners