SLOWLY take the schrader valve out of the fuel rail- it will leak gas, so have rags ready-, put a 3/8" hose on the rail. Put the end of the hose in a bucket or something. Behind the alternator, you will see a wire with a spade on it, just hanging there. Take 12 volts to it- back of the alternator at the stud works- and the fuel pump should run and drain the tank. I use clear hose so I can see the bubbles when it gets low.
Interesting note: When I detailed cars at a chevy dealer, the mechanics always dropped fuel tanks when they were patially filled. I asked why you wouldn't just drain them so they'd be lighter? They said that fuel VAPOR is far more explosive than liquid, and it was safer to do it full. Just heavy, though. Makes sense, so I do mine half full, no boom yet...