I have a 1988 GMC 1/2 ton 4x4 with a coolant leak. When I pour water into the radiator, it pours out of a hole at the bottom of what I think is the transmission bell housing. It looks like there is a plug of some kind that has popped out. The hole is about the size of a bb and is really clean as if it has been machined.
Any thoughts?

Could be the waterfitting which the factory piece was made out crappy pot metal.Watch out it will break and it is a pain to get the rest out of the intake.The replacement is made out of steel.It can be intake gaskets also.

What motor ? 5.0and 5. 7 have 2 freeze plug at the back of the block next to the cam plug.