A suggestion on metal prep:

Many products require a water rinse after application. These are a little harder to get the residue off.

I use an R&M product that containes alcohol, and does not require rinsing. ( 801 Metal Prep). Just wipe it off while it's still wet. If it has dried, rewet it and wipe it off. It will leave very little behind. I always follow with a wax and grease remover, though it might not be necessary. I was told this neutralizes the acid.