This is how i use it,i dont bother with two buckets anymore
You can pre rinse first, but the foam wont sitt on the car aslong
Snow Foam car then let it dwell for 10 mins then rinse off
If its realy dirty i would foam and rinse twice
Then foam again but this time i would take a mitt to it and have one bucket with clean water to dip the mitt in after each pass
Some use snow foam then use the two bucket method