Tank may have a drain bolt, so check for that.
Starting the nuts by ever so slightly tightening them, spraying more fluid in, and then backing them out till a little more tension builds.
Get them to move a pinch of a turn at a time as they are coming out, then spray, then back in, spray, back out,spray. You get the idea.
I do this god knows how many times a day, and unless you can clean the threads above the nut with a wire brush or something, this is the only way to help
get the crud washed out, or the crud will cause the nut to jam and take the stud with it.
If they are going to come off they will, if not ... well yeah.
I've been looking at the new tool off the MAC truck that uses a larger wire and electromagnetic head induction (or whatever he said), to super heat whatever you wrap in the wire.
Got a bolt red hot in under 30 seconds. Would be great if that tool could get sent around the country to help those with rusty fuel tank bolts! Don't ask how much it cost though. /ubbthreads/images/graemlins/banghead.gif