If you don't want to blast use cheap brake cleaner in a spray can. I removed the black paint off of a aluminum engine I have on a motorized bicycle..Picture if you like. Tanks would definitely be easier although the engine wasn't hard to do. I sprayed it on and used a artist paint brush to get all the nooks and crannys. Use the brass brushes China Mart sells 3 for $3.00. Finish with a soap pad and water. Set the tank upright and let the cleaner run to the bottom. All the paint will soften or should soften up and remove with brass brush.
By the way..use eye protection as that crap WILL burn the eyes. They also make a paint remover/stripper
http://www.google.com/products?hl=en...ed=0CBgQrQQwAAespecially designed for the aluminum on aircraft. Home Depot has it I think.