Do yourself a favor and buy a Fluid Evacuator.

You can drain the radiator without spilling a drop. It also works great for draining automatic transmissions before dropping the pan, bleeding brakes, and a whole bunch of other stuff.

 

You will only get about 55% to 60% of the coolant out with a simple draining from the radiator. You will need to refill and drain 3 or 4 times to get the old stuff diluted sufficiently.