if there's real 'crud' a good rinse will get rid of it [if it's impacted, use a high pressure hose], if you mean the black surface, that's the color of the converted metal and it won't change, the previously rusted areas won't get looking like "new" again, which is why afterward you need to use the sealer/sloshing compound, same as you'd have to use primer and paint on body panels - if you try to get it all perfectly clean you'll wind up eating the metal away like your electrode
also you shouldn't need to replace the solution, just settle out the particulate and re-use it, it's effective almost indefinitely
Bill
