[Walt Fricke]

Yes, the return line goes through the tank directly to the filter. Oil which gets past the filter drops right down into the tank. However, I bet your spare tank doesn't have a filter installed? I have never tried to blow through a filter, so don't know how restrictive that is to lung pressure.

Changed your filter lately? The Porsche recommended filters have a bypass feature, so, if they get clogged, oil (unfiltered) still can get through, so there is something returning to the tank, and you aren't getting a huge overpressure. A filter without the bypass feature could clog and greatly increase resistance.

Hard to imagine anything large enough to block any of this happening without you knowing it, though. Hard to miss an engine blowup.

Swapping tanks isn't all that hard a job.