Re: Giff Marr's question:

In my humble opinion, the conduit material should be slightly flexible
(unlike an aluminum tube) to allow for the inevitable wing flexure without
overly stressing (and possible failure) of the bond at the ribs - which
would probably result in a fuel leak, big time. Since the ribs are
completely bonded around their periphery, they are probably too stiff,
laterally, to allow much give when the wing flexes, thereby putting most of
the stress on the tube-to-rib bond.

On my early 235, I put the wing fuel between the spars in the inboard
section of the outer wing. As such, I also had to put a push-rod tube
through the fuel bays. I built them of fiberglass (about 2" diameter, about
three layers) around a cylinder of foam, later dissolved out with solvent,
and installed between the ribs. After installation, the tubes were sealed
with the the same tank sealer used for the tanks and have been leak-free for
over ten years.

Dan Schaefer