One of the two nipples is an over flow and the other is for oil injection which yes can be blocked off, the screw on top is not really a screw it's a plug that allows access to the power jet.What is the 2 nipples for in the back and what do they do. And do I plug those? And what’s the screw at the top on the inlet for. It says for negative pressure. But didn’t no what it was used for cause there’s an adjustment screw there too ?