I think Mr. Reher is not considering all the variables. As Charlie says, the pump is sucking from the same reservoir it's pumping to. The oil is being sucked from the mains/rods/cam bearings by the same "vacuum" as the pump pickup sees. PCV valve will mod this some, but a GOOD manifold vac is under 20", and only applied at idle, when the lube requirements are at minimum. I think you'd have to have one heck of a vac on the sump to pull a vacuum bubble in the pickup, and I LIKE a good ring seal...