Pay attention to what @Mark Jennings is saying. Vented gas caps are for letting air in to avoid vacuum. They are sealed for air (or fuel, like in a roll over) trying to get out. That’s what the weep hole is for, to keep pressure from building in the tank and then possibly rupturing something not intended to be ruptured. Also, as pressure goes up in a fixed volume the temperature must rise, generally not desirable with fuel. The weep hole is not a bad design, in fact a good simple and functional design. When the environmentalists forced the emissions controls the designs went from simple and effective to complex and less effective (or rather higher maintenance required). So don’t overfill your fuel tanks, simple.