Disconnecting the lower pass. hose is quick, but messy. I've also cut petcock access hole in the air dam like glock20man suggested, but usually just remove the black plastic air dam and set it out on trash pickup day.
I know "I'm late to the party" but here is another 2 cents worth:
If you don't know when the last time your coolant system as been flushed/drained or you see rusty crap in your coolant reservoir, then I'd suggest removing the RH lower hose RATHER THAN messing with the radiator drain valve. I've had crud plug up in the drain valve and then I COULD NOT CLOSE THE VALVE because it had crud stuck in it!