Decommissioning Septic Tanks

Learn about the situations when decommissioning a septic tank is mandatory and the steps you need to follow.

Understanding decommissioning

When  sewer connection becomes available to a property, the property must connect to it within five years. If the property is sold, the sewer must be connected within one year of the settlement date. Septic tanks should be decommissioned soon after the property connects to sewer to prevent them from collapsing in the future, which could cause damage or injury.

The decommissioning process involves a licensed liquid waste contractor emptying all septic tanks, soakwells, and leach drains. After emptying, these components should either be removed or broken up and filled with clean sand.

When is decommissioning legally required?

The City advises property owners to decommission onsite effluent disposal systems soon after connecting to a mains sewer. By law, septic tanks must be decommissioned in the following situations:

  • Upon purchasing a property: New owners must decommission the septic tank within 60 days of ownership. This is often addressed during property settlement.
  • During construction: If building work is within 1.2 metres of the septic tank or directly above it, decommission the tank before starting.
  • Change in property use: When converting the property's purpose (for example, a home business), decommission the septic tank within 60 days of the change.

Steps to decommission your old septic system

  1. Hire a licensed liquid waste contractor to empty the septic tanks, leach drains, and soakwells.
  2. If feasible, remove the emptied components. Removal is especially important if you intend to build something in this area.  If not, break up the septic tanks' bottoms and lids. Fill the cavities and components with clean fill, such as yellow sand.
  3. Compact the fill thoroughly for stability.
By adhering to these steps, you'll ensure your old septic system is decommissioned in line with regulations and safety protocols

More information and contact

For more information on decommissioning a septic tank, contact the City’s Health Services team on 08 9411 3444 or email [email protected]



City of Cockburn
Whadjuk Boodja
9 Coleville Crescent,
Spearwood 6163

PO Box 1215, Bibra Lake DC,
Western Australia, 6965

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Cockburn Nyungar moort Beeliar boodja-k kaadadjiny. Koora, yeyi, benang baalap nidja boodja-k kaaradjiny.
Ngalak kaadatj dayin boodja, kep wer malayin. Ngalak kaadatj koora koora wer yeyi ngalang birdiya.

City of Cockburn acknowledges the Nyungar people of Beeliar boodja. Long ago, now and in the future they care for Country.
We acknowledge a continuing connection to land, waters and culture and pay our respects to the Elders, past and present.