I'm familiar with the assemblies your speaking of. Trust me, these arn't even rejects from Parker.
What the tank builders are doing is fabing the Ell with a 1" long arrow shaped barb. Then a poly, nylon derivative tube is forced over the barb. That's it, nothing else. They count on the mechanical fit between the larger barb end and the smaller shank diameter tube to seal. Unfortunately over time air will be allowed to enter the system at this interface. It's more of a problem in tall tanks
than short. I can only guess it's the mechanical advantage of the fuel
sloshing around moving the longer pick up tube.