I suspect the engines with no broken rings will produce little unassisted venting - that is, venting without the suction via engine vaccuum.

I also suspect that when this setup is in use, most of the crankcase venting occurrs from the lower hose into the case.

.....which brings up a question: Exactly HOW is the upper & lower venting setup built inside the tank?
> How low in the tank and in what fashion is the lower vent constructed???