We don't see that as much these days as we did in the '70's and '80's, but that's probably because by now many of our trucks have had the old rubber hoses replaced at least once.
I blew air through the vents and tubes, could not detect any kinks or obvious restrictions, but replacing the hoses with new ones completely eliminated the issue for me. Never came back either.
The old debris/dirt dauber theory is very likely, as I never actually opened my old filler hose up to see, but the new one fixed it.
I had already replaced my fill-vent hose prior to that with zero change in the tank's bad attitude at the pump.
Never had the problem with any of my aftermarket tanks either, but they were all accompanied by new hoses as well.
Only time I saw anything like that was on a NWMP tank when the guy installing it looped and kinked a too-long fill-vent hose instead of just cutting it to the correct length.
After cutting and straightening it, the issue went away.
Paul
