I haven’t yet looked into whether car washing in strata is banned or not in NSW. It isn’t banned in QLD. However, you may not be aware that House Rules are not enforceable. Instead of House Rules, the car washing directives should be inserted into the By Laws and approved via a vote at a General Meeting. What do your existing By Laws say about car washing? Perhaps you can propose some more environmentally friendly directives for car washing via a Resolution at your next AGM. Worth a try?