Replacing gas tank in my '65 Dart...

The tank is held by the strap and is a slip fit onto the filler tube with a rubber donut looking gasket. As said, remove gas, remove strap and start wiggling her off the filler tube. BRass mallet or punch on the sender ring. Once you get it off and drained, put some pool acid or super radiator flush in it and some pachinco ball in there (or big ball bearings or sling shot ammo) and shake it all around. the balls help dislodge the rust and crud. If that is not doable, then a brass grill brush hose clamped onto a piece of pipe. Get into the sender hold and start scrubbing the bottom. Then a trip to the car wash or high pressure cleaner. There is a tank cleaner/sealer you can buy that supposed to do it with less effort but if you got it out, nothing beats a good physical cleaning followed by the wash. get yourself a new sock for the pickup and run a plastic filter inline with a metal filter (plastic first) so you can see what is going on. That gas you siphoned smells like thinner? Put it into your lawn mower or slant six, thats all its good for (and youll have a heck of a time starting those too)