I used Molasses in my Honda sl350 tank that had a fair bit of rust in it i mixed about 10 to 1 ratio, left it for about 3 weeks checking it regulary, after that i flushed the tank out with water, then flushed with fuel , it came out new , if the tank looks sound dont cream it, just put fresh fuel and a touch of 2 stroke mine is still like new that was over a year ago.
Molasses is the best way and the cheapest around $10 from a grain store, hope that help ya