Inspect the septic tank system yearly for levels of sludge and scum. You will need to call in a company to remove sludge and scum when floating scum is 75 mm or less from the top of the outlet or sludge build-up is to within 250 mm from the bottom of the outlet. (Auckland Council recommends that when the combined level of scum and sludge in the septic tank is 50 percent of the tank volume, it is pumped out.)

For many households this de-sludging will be approximately every 3–5 years, but the timing depends on the age and capacity of the system, how many people use it and what goes into it (ideally nothing beyond sewage and toilet paper, and definitely not solid items like dental floss or cigarette butts).

Apart from assessing sludge levels, servicing should include inspecting pumps and pipework and cleaning as necessary, inspecting tank inlets and outlets, checking and flushing the irrigation area and then communicating everything found to the householder.

Auckland Council requires that all wastewater treatment and disposal systems in its area are serviced at least every six months. Companies carrying out servicing will provide documentation the homeowner can use as evidence that they are complying with the council requirement.

With land application areas, householders can redirect effluent at the diverter (if one is installed) every six months. Some filters can also be cleaned and replaced by homeowners.

Auckland Council has useful maintenance information downloadable here.

The New Zealand Water and Wastes Association also has good information downloadable here.