The one in the middle is the drain/fill, and the one to the side is the vent.
SO... with both out... the oil should drain from the center... but you will always get a little out of the vent.
FYI... the oil is think, and sometimes will get stuck, and won't drain. I would put a hose into the side hole, and blow into it. That will help push the oil out.
Then... put the pump into the middle hole, and fill the case until you get some oil out the vent. Should be a little less that a quart. (27~28 oz)
Put the vent screw back in... and then remove the hose on the fill. Plugging the vent will keep the oil from draining while putting the fill plug back in.
MAKE SURE TO USE NEW BLUE WASHERS !!