didnt say what truck ya have. But I'll assume its a k5, and its Fuel injected, since you have an in tank pump. So here's the easy way....
there is none. its a PITA, unless in your infinate wisdom, you installed a drain valve. If you did not...
Your gonna have to get that fuel out. If you have a power pump, get some jerry cans ready. Suck it allll out
Unbolt the skid plate if you have one.
Then undo the straps, while keeping the tank supported. Carefully lower it ever so slightly, so you can undo the lines. Be very careful, as too much movement can snap/damage/cause leaks. (be a good idea to spray it down with pb blast or something). Support the fittings, so you dont twist the fuel line. After all lines (and power) have been removed, you can get the tank out.
A buddy or two helps this process ALOT.