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.

Problem	Solution
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

Updated: 13 December 2024