It could possibly be a garden hose hook up to flush the motor(?). OnlineMicrofiche Index has schematic drawings of your motor. Just pick the make/model/year and you can see the schematic of what (if anything) goes there. There will be an associated part number as well.
That's a crankcase breather. You can google what it does, but it's mainly to ventilate air. There shouldn't be any water or oil in it -- which is a good thing. There should have been a picture of it on that website under the crankcase section.