The question is how much rust? Ideally you want it gone, but after sandblasting I have found areas where the metal is pitted and the rust is gone in all but the deepest pits.
No one wants to do something twice, but you also have to be realistic about the situation. I have used Dupont 5717s etching wash and Dupont VariPrime with success for minor pitted spots.
Same situation with the pitted metal, I am experimenting on a project with epoxy primer. We will see what happens...
Again be realistic about the situation, treat it the best you can, then seal it up. Most of our pumps and such reside indoors these days. If its sealed and there is no moisture there will not be a rust problem. Rust needs oxygen and moisture to blossom!
