Rusty gas tank

I'm working on a car now thats been sitting for a few years. Yesterday i pulled the tank off cause the p.o.s. fuel pump doesn't work from where its been sittin and the tank seems too have a great deal of rust in it. How in the hell do u get that out. My grandpa was an ol school shadetree mechanic and he used to put rocks in it and shack it around o break loose all the rust. But i'm too lazy and am looking for other suggestions!! Thanks in advance
 
Agreed. A new one is a better bet than restoring the old one (POR15 and Kreem are not cheap).

FWIW, parts stores can often order tanks as well.