Interesting reading the ferry fuel system on the register. Yes, that generally describes the system I have flown twice in the '80's. Yes, the cabin ferry fuel will drain into the airframe belly tanks by gravity. I don't remember the exact details of the venting, but it is very memorable my captain being in the cabin for 45 minutes cursing at it while he tried to clear it. He succeeded, and we continued as planned. That leg of the flight was 13 hours, Rotterdam to Rhodos, Greece.