'00 yz426 - Threaded Hole Under Water Pump?

Just bought the bike a few weeks ago and finally got around to using the other day. I noticed I have a coolant leak coming from a threaded hole under the water pump in the crankcase cover, the tiny bolt is obviously missing. I've checked the manual and there is no mention of a hole being there so I have no idea what size bolt it requires. It's location is under the pump where the protrusion in the case from the pump forms back into the crankcase cover, if that makes sense. Is this a factory drain for the water pump? Does anyone else have this drain? The hole is about a quarter inch in diameter.

edit: I looked at it better, its not threaded.. Has a flat surface surrounding the hole. Some kind of rubber plug maybe?

Edited by rokyholler

And the hole faces straight down? No bolt or screw goes there. That's the escape port to allow coolant leaking past the impeller shaft seal to escape to the outside instead of contaminating the engine oil. If you have a leak there, you need new water pump seals and possibly a shaft:

http://www.thumpertalk.com/forum/showthread.php?t=940018

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