Rustay56 makes a good point. For you to do it successfully and somewhat efficiently you'll have to spend a bunch on materials, and you'll still have to work your ass off.
If you insist on doing it yourself, do it just like a paint job - use sandpaper in fine then finer grits, use every step in the grit sizes available - and use sandpaper as long as possible up to 3000 and higher grit. Think about what it takes to do stainless trim, most of that stuff that's in good shape still requires a lot of work and those pieces are tiny compared to your tank. The big difference between paint and polishing metal is that the metal can stand far more wheel speed but needs that to make progress at all.