Some cars have a drain plug at the bottom of the tank. Get a large container and drain it. You may have to stop it mid-stream so be prepared to smell like gasoline. You may have to filter it out as well.

does it have a solid tube from fill port to tank or a rubber hose conecting them? if hose can take that loose and get in that way. might be easier to drop the tank though and pull sending unit out and get in there, esp. if your going to junk the car most places make you take the tank down anyway. just have a jack and someone to help steady the tank they are heavy and tip easy when full.