Never used it on washers, but use it on cars all the time. You don't have to use the 3 steps, however, the cleaner the surface, the better it sticks. I had some metal bits sandblasted and the Por finished like glass.
Por (paint over rust) will stick to rust just fine. Scrape and sand all the loose stuff and have at it. Make sure you wear gloves. If you get it on your skin, no chemical will remove it. Your skin must naturally exfoliate it.
Finally, you don't have to paint over it unless it will be exposed to direct sunlight (read: outside).