Just put in rebuilt 12a and started putting water in to test cooling system and water started pouring out of this little coolant port at the bottom of the centre iron. I can’t find a diagram that tells me what goes there.

 

that is where the coolant drain plug would go.. its the same thread for every rotary, i think its 8x1.25, but you can see its got a big head for a washer

 

Thank you so much! Glad I'm not missing a sensor or something

 

The factory bolt is small in length and also has a crush washer,