"For flights arriving into Australia, passengers may purchase duty free liquids, aerosols and gels of a greater capacity than 100ml if they can be delivered to the boarding gate in a sealed bag with proof of purchase. They can only be collected by the passenger after proceeding through the screening point. Further, passengers may purchase liquid, aerosol and gel duty free items onboard an aircraft, but should note that in some instances these items will not be permitted to be taken through transit screening points"
There is a duty free shop in Perth Airport that you can access before immigration, saves you the hassle of carrying it from Dubai.