This is the fuel tank used in the C5 A6 Quattro and Allroad. Multiple level senders, an internal siphon system to transfer fuel between compartments, and a hole in the middle (for the rear differential). I am in equal parts horrified, in awe, and completely unsurprised.
This may explain the extreme nonlinearity of my Allroad’s fuel gauge... Between that and the 2.7T’s incredible thirst, anywhere below 1/2 means “fill the hell up NOW.”