What I do is take the radiator cap off and put a small rubber hose in the radiator going to the bottom and syphon it out. It works as well as draining and I don't have antifreeze all over the suspension.

 

in the 2004 GM Service manuals (GMT/04-CK8PU) Volume 2 of 5, page 1838 and other places, it says to place a pan under the lower hose, and remove the lower radiator hose from the radiator. No mention of a plug.

A good siphon hand pump will work wonders, and the coolant could be easier to re-use because it didnt spill all over other things before going in a pan. If you didn't need to replace the coolant anyways.