Step 4: Empy the Tank
Shake the tank to make sure there is no liquid propane left in it. It is a good idea to attach it to a propane appliance and keep the valve open for a while to make sure there is no resididual pressure in the tank.
As a mater of good practice, remove the valves before drilling into the tank. A small pair of needle nose pliers, or hemostats, can be used to unscrew the pressure relief valve.
The pressure relief valve (the one to the side) is the easiest to reach. It is not necessary to remove the main center valve because the whole threaded tank fitting will be removed; valve and all, in a future step.
(Also, The valve in the center is more difficult to remove; requiring removal of an inner plastic sleeve and an O-ring before the schrader valve can be accessed.)