How does a septic system work and what maintenance does it need?

An on-site wastewater system has two parts. The tank settles solids and holds them while bacteria break them down. The liquid then goes to a land application area, a trench, bed or irrigation field, where the soil does the final treatment. Almost all failures are in the second part.

Maintenance that matters

• Pump-out on a cycle, commonly every three to five years depending on tank size and household size. Sludge that reaches the outlet goes into the disposal field and blocks it permanently.
• Aerated systems have mechanical components and usually carry a mandatory service contract, often quarterly, required by the local council.
• Keep vehicles, stock and structures off the disposal area, since compaction destroys it.
• Keep stormwater away from it. A downpipe or a driveway discharging over the field will overwhelm it.

What kills a system

• Wet wipes, sanitary products and fats, none of which break down.
• Excessive bleach and disinfectant, which kills the bacteria doing the work.
• Very high water use in a short period, which pushes liquid through before solids have settled.
• Tree roots in the disposal field.

On-site systems are approved and regulated by local councils, and approvals attach conditions including servicing. If you have bought a property with one, ask the council for the approval and the service history rather than assuming.