Yes, washing is okay and the about the best way to remove all of that sanding dust. A good, grease cutting, dish soap (I use Dawn) is fine as long as you rinse it off very well. Also make sure it is well dryed before you spray anymore paint. I use an air nozzle and blow as much water off as I can before is sits too long. And ALWAYS wipe the surface with a good degreaser like PrepSol or Pre-Kleano before spraying any paint.