Agreed that it can be a PITA, but to answer the question.
There is a drain valve on the drivers side of the radiator. It's accesible from the top or bottom and depending on the year of your car, it's either a tab that usually breaks off when you use the pliers on it, or a slot that accepts a 1/4" square drive ratchet. The plug takes about a 1/4 of a turn and stops, at that point it will continue to turn but at the same time it needs to be persuaded in an outward direction. Once it has turned out to the appropriate position the coolant will drain cleanly out the bottom of the radiator with no mess.