Reconnect the gas line at the tank, and remove the inlet line at the fuel pump. Put a VERY slight amount of air pressure into the tank to get the fuel started flowing, and it should siphon the fuel level down to within a couple of inches of the bottom of the tank. Then remove the tank, and do a thorough cleanup with a pressure washer, or some other way to get rid of all the accumulated crud and varnish from the old gasoline. I've been known to ratchet-strap a gas tank to a rear wheel on my tractor, throw in a couple of shovels of pea gravel, and bush hog one of my pastures for an hour or two.
Jerry