To prep the surface down to remove all contaminents I would wash to remove all suface dirt and grime. Wipe with vinegar to remove all wax and any other sealants. Wash with car shampoo, rinse, do not dry and use car wash mixture to clay with instead of the detailing solution they provide with the bar. Rinse to remove all suds and wash again for good measure. You can omit the last wash and just dry after the rinse.