I'd like to drain my radiator but don't want to let the old coolant spill on the ground

*AND* I want to get the old stuff into a couple of new containers - I expect about 3 gallons total.
I'm thinking maybe I could use some kind of a valve that would screw into the drain hole like the regular radiator plug does and then attach a plastic hose off of that which I could use to control the liquid coming out

.
Maybe a hardware store might have some kind of valve? Does anyone know the size of the hole that the radiator plug screws into? Any other ideas for a good way to control the flow of the old fluid out?
Mike
1985 300D
Blue Black Metallic