Evinrude fastwin weep hole... what is this one?

Hey guys, first post here. I bought a 1963 fastwin 18 and after the first run I noticed a greenish color substance coming out of one of the holes on the lower unit. The oil looks okstill. But my question is what is this for? It's the one in the attached photo between the words this and hole. NOT the ones the arrows point to. That's a photo I got online it's not mine.

Doesn't look like my picture posted. It's the hole farthest back from prop between the two flathead oil fill holes.

No photo.
With no pic I would guess a drain for the lower cavity.