Last time I did this I drained the radiator and then took off the theremostat housing and used my shop vac to suck out the rest of the water. If I remember right I also took out the lower bolt on the alt. bracket that goes to the head on the pass. side and that helped drain the head. You'll never get it all out but that will get most of it, also watch that you don't spill any of the antifreeze down the exhaust pipe like I did , it sure does make it smoke at start up.
1956 Ford F-100 460/C6
1964 Galaxie 500/390