Wanted to let you guys/gals know that 'The Works' toilet bowl cleaner DOES work for cleaning out tanks, rusted, grimey, etc. I've done three tanks (and so have some other forum members) now and was skeptical at best. This stuff does what it says. Costs under $2.
You can google the method, but in a nutshell,
remove tank
empty tank
remove petcock
remove fuel sending unit
tape or plug up those holes
empty 50% of 'the works' into tank
fill remainder with water
allow to sit for 15-20 mins
shake and twirl to coat inside of tank
add more 'the works' if needed
allow to sit
drain
rinse with water
coat with acetone, gas, or a water absorbing liquid
allow to air dry for 24 hours
put gas in
go ride