Finlay tracked down a Car Cube 12 v pressure washer not easy to find in Airlie Beach, but available from Auto Barn and a few other Auto parts retailers nationally.
Just gave it a test run and am happy with it, it's not a huge pressure (180 psi) but is plenty good enough for washing down the Yak and rods reels etc, with a good adjustable jet spray. It will also double as a cool fresh water shower on a hot day.
It takes 13 lt to fill it and is very economical on water Probably around 3 - 4 lt per wash down so it meets all the criteria for local water restrictions. Been looking for one for a while now, it'll be fantastic when launching the Yak in some of the more remote places, great for getting rid of all that sand and grit not to mention salt and fish slime, and it'll keep all the salty crap of the roof of the car.