[dad911]

Thinking about it, I have seen vent lines run along interior roof of the car/rollcage that terminate in a front oil tank (which had a vent)

So in this case, the oil tank collected drains back into the tank.

My mechanic also had a turbo motor where he tapped the valve cover with a small fitting and attached the drain line from the catch can (mounted high) to the valve cover. Leaving the valve on the can open, the catch can always drained back into the engine.