I've read the archives on changing the coolant, but I'm unsure about draining the coolant from the engine block on my '98 E320.

I found what I believe to be the drain plug. It is on the right side (passenger side), between the motor mount and exaust manifold. It appears to be smooth all the way around, so if this is it, how should I loosen it? Is there a trick to draining the block?

Thanks in advance.