Decommissioning Septic Tanks

What is decommissioning?

Once a sewer connection is available to a property, it must be connected within five years of the water corporation advising of its availability. If the property is sold, it has to be connected within one year of the settlement date. Septic tanks must be ‘decommissioned’ to prevent them from collapsing in the future and possibly causing damage or injury.

Decommissioning means that all septic tanks, soakwells and leach drains are pumped empty by a licensed liquid waste contractor. All empty septic tanks, soakwells and/or leach drains must be either removed or have their lids and bases broken and filled with clean sand.

When do I have to decommission a septic tank?

The City strongly recommends that onsite effluent disposal systems be decommissioned soon after a property is connected to mains sewage. Under law, septic tanks must be decommissioned:

  • Not more than 60 days after ownership of the property has changed. New property owners are responsible for ensuring that septic tanks are decommissioned and are advised to obtain proof. This process is often negotiated during property settlement
  • If the foundations for a building on the premises are to be built closer than 1.2 metres from the septic tank, or a building is to be constructed above it
  • Decommissioning must occur before any building works commence
  • Within 60 days if there is a ‘material change of use’ of the property. For example, if a residence is turned into a business, the system must be Decommissioned not more than 60 days after the change of use has occurred.

How do I decommission my old septic system?

Septic tanks, leach drains and soak wells must be completely emptied by a licensed liquid waste contractor.
Empty septic tanks, leach drains and soak wells should be completely removed from site if possible. If it is not possible, the lids must be removed and the bottom of septic tanks broken up.
The excavations, septic tanks and leach drains or soak wells must then be filled with clean fill such as yellow sand, and then thoroughly compacted.

More information and contact

For more information on decommissioning a septic tank please email us or call 08 9411 3444.



City of Cockburn
Whadjuk Boodja
9 Coleville Crescent,
Spearwood 6163

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

Office opening hours:
8.30am to 4.30pm
Monday to Friday (excluding public holidays)

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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, present and emerging.