Only ever use a single bucket to rinse the sponge.
All done with hose and (now) power washer but never on high pressure.
Its not rocket science is it?
Wash wheels first. Hardest part! Normally do two cars in tandem for this bit.
Then, rinse off as much muck as possible, snow-foam using attachment (ace - whole car covered in seconds), leave a couple of minutes, wash down with microfibre sponge rinsing it out every panel start at the top (well, as high as you can get on a Zed) and work down the panels, rinse and then dry with microfibre cloths, then, if there's time, wax and polish with superfine microfibre cloth. Next car...
All done in 40 minutes each tops. Takes an hour to get all the equipment out and put it away again though
All cloths etc get washed afterwards - never left or re-used.
Am sure theres more refined and probably better ways, but it works for me.