I attempted to pressure wash my garage floor today, it's sealed concrete with a few years worth of working on cars gunk all over it. Paint overspray, body schutz, oil, grease, etc... I have a 2000 psi washer I borrowed from a friend, the single stream tip would barely remove the tough spots. Now that I have the garage cleared out, I would like to get it clean. Any ideas for a cleaner to put down or cleaning method?