I got a 80 thosand CC Ironhead chopper with a homemade stainless steel oil tank. The tank has three fittings. One above the bottom to feed the oil pump, one close to the top for the oil return, and another one next to the top for a vent. When mounted in the frame the tank angles a bit putting the return fitting a little below the vent. I just need to know how to fill the tank. How far below the vent must it be? Must the oil level be below the return fitting?