Hi, Does anyone know the best way to remove rust from the water passages of an engine block? I know that hot tanking doesn't remove rust.

This block is already out of a truck, so I can't use radiator flush. How about putting it in a small tank in a solution of "Iron Out" or would that eat to much metal from the cylinders? I know that phosphoric acid will eat metal. What else can be used?

Thanks for the input.
Steve