This is on a 68 dart. It has a very small maybe 1/8” hardline that comes off the side if the filler tube near the top. It winds around in a circle and then follows the filler tube down and through the rubber gasket that’s screwed to the trunk floor. But I’m sure after 50 years that it could be plugged up. I know back when I was driving the car regularly with the previous engine, when you pulled the cap off to fill it up, there would be a big rush of air, either going in or out. Don’t really know.
