Bob,

It's been one whole year now and about 20 gallons gas through a few and various set-ups. Tygothane is still as good as new. No swelling, no crazing, no hardening, inside the tank or out. I also use it inside and outside on the main gasoline jug I use.... In contrast, the yellow Tygon for gasoline has been replaced a couple times in some areas. I have nearly eliminated the yellow stuff from my equipment.

Urethane is one of the toughest plastics we have....abrasion resistance is another strong suit. No downsides seen yet. As a matter of course, I tend to use either a small tie wrap or shrink tube to secure fitting ends

Neoprene from the LHS is no good at all eventhough it should be. The stock my LHS has, apparently was extruded without anti-oxidants. In 3 months the stuff crazed and eventually leaked around various barbed fittings.

Of course, Viton is the best of the best for our application but at about 4$ a foot, it's 10X the cost of Tygothane. Also, have not been able to find soft and flexible Viton (haven't looked very hard tho). I'd settle for thin walled to produce flexibiliity but the thinnest has been 1/16" wall and that's a bit too stiff. I've made a clunk line from Viton by grinding the wall with a dremmel sanding drum and it worked but it was a pita.