Inverted fuel plumbing

[Mjpierce1]

I purchased the inverted fuel kit in 2004 and now am getting around to plumbing it. For some reason, On the top of the upper rear fuel tank I have welded in another opening for a fitting - not sure why and I don’t remember doing this, but may have at the same time I had a smoke oil tank fabricated. I only see two openings in the drawings for the upper tank, the filler opening and one opening for the air vent.

I’m confused on how to plumb the air venting, and don’t understand how the system draws air when inverted.

If anyone could illuminate the air vent plumbing for me, and confirm that the upper tank does not need the additional opening I had welded in I would be grateful. Thanks! Martin