On the ST models I think you have to drill the rivets out of the dash that hold the tank bracket in place. There will be carriage bolts towards the front that hold the two tank bands together and they will have to come out, too. To clean out the old goop I empty as much out as will come out, then spray about half a can of carb cleaner into the tank, throw in a half-dozen 1/4" X 3/4" bolts (I save them, they're special) and shake the heck out of the tank. Eventually, the inside of the tank will be pristine.
There should be a bulkhead connection at the left top of the tank that the fuel line attaches to, and the pick-up is attached to a shorter line on the other side of the bulkhead. The other end of the short line is attached to a brass pick-up that sits at the bottom of the tank. The fuel line usually goes to a shut-off on the dash, then through the left side upper body cavity and back to the fuel pump.
Hope this helped.
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far