I have tried just about everything. All the things posted here. But, I never tried the 1/4 nuts on a string. That is smart. Without the farm equipment to shake the tank(not a farmer) I have used an old swamp cooler motor with a weight bolted to the pulley. My version of a shaker. Strap to the tank and let it rattle the gravel and it comes out nice and clean. Getting the gravel out...is a pain. Nuts on a string..that is genius. Epoxy in the tank. Gotta be better than "Cream" that I used in old motorcycle tanks. New fuel messes with everything. Never did figure how to get rust out of the seams. Used 2 fuel filters, one just after the tank before the fuel pump and one just in front of the carb. Used the glass see through types and took them apart often to keep that crud out of the pump and carb. Epoxy seems a better idea. Older tanks have a bottom feed and a drain valve. Up to about 54 I think. After that the fuel feed is at the top of the sender. The sender is the same. The screw pattern is the same. So I have run them in my truck(52) just cap of the fuel line on the sender. There is no way I know of to clean out that varnish like stuff without removing the tank. And with the top fuel outlet, you have to siphon out as much as you can. No drain. Old gas is evil. It can stick valves. Clog pumps and mess up the carb. So I have learned to get it out and get it gone. Good luck with yours and let us know how it goes.
