In the video I posted above you can watch the filter fill with vapor under pressure as the engine is running. (Ideling in the driveway after a drive 75 to 85deg day.
In my dart 273 2bbl the filter would go empty, the pressure between the filter and the carb would stay at 5 to 7 for a bit then drop to about 3 as the engine would start to idle down in RPM then an inrush of fuel and the rpm would pick up.
That is on alcohol laced fuel.
Does not happen on non alcohol fuel.