Getting the tank drained can be a challenge. After you've disconnected the battery, Make sure all the hoses and electrical are not attached. The Fuel filler neck will be a bit difficult, there is a way to twist it after removing the fender screws and I think there is a strap brace too on the filler neck. Part of the Ford recall fix for the gas tank explosion issue was a longer filler neck that went into the tank further, that does complicate the removal. If you look underneath, there'll be two bolts attached to straps attached to the unibody behind the rear bumper valance. Remove those with a floor jack and plywood under the tank. If you can't get the filler neck out first, Make sure the car is high enough on jack stands to allow the tank and the filler to clear the bodywork, Move and twist the straps 90 degrees and they should fall out of the unibody along with the plastic shields near the rear axle. Pay close attention to how all this is removed.
Once you have the tank out from under the car , make every effort to drain any remaining fuel safely. There may be a locking ring holding the Fuel sender unit to the tank, It may not remove easily, usually a brass drift punch to turn it 1/8 turn to release. The filler neck pulls out of the rubber grommet in the side of the tank, It (grommet) may disintegrate when you attempt this, it's usually a throw away item during this work.
If the rust is bad... Count on the possibility of a replacement and you'll probably lose the fuel sender/pickup too. There may be a cross reference for another Ford model of this part. NOS is near impossible to find for this piece. My filler neck had rust for quite a bit of the length inside the tank. Another piece to research availablilty.
This will get you started..
Pintosopher