No you can't dump other people's property. And good for the police pointing this out.
Have a read of DISPOSAL OF UNCOLLECTED GOODS ACT 1967
http://www.austlii.edu.au/au/legis/qld/consol_act/douga1967285/
Just contact the local police and tell them you have a court order for an eviction and you want to arrange for some police to go over and force the tenants to leave.
