I had a very bad maxi tank once....it was rusty, but it was also super crusty. I took a handful of 1 inch drywall screws and hot water/degreaser and shook the crap out of it when I had it disassembled down to the frame. The sharp screws broke apart all the debris, and what came out was chunks of fossilized gasoline/lacquer and gunk about the volume of a baseball, some chunks the size of a ping pong ball.
I probably would have never gotten that out or know about it without the screws, and would have been doomed to a life of inexplicably dirt gas. Cant seem to find the pictures though.