Basically the same as you would try to pull yourself out of the water on your own hair.
Venting is basically not for exhausting fume it is moreover for avoiding a vacuum in your tank to allow fuel still beeing sucked out by your pump.
Your idea would work if you would have a vented cas cap ( but than you wouldn´t need any vent line either).
So if your cas cap is not a vented one you need an external air supply to the tank.
Best way to do it is with a vent valve.
Aero Tec Laboratories, Ltd. Racing Fuel Cells - PRODUCTS - Vent Valves
INLINE BREATHER/VENT VALVE 5/16 PUSH ON
and than run the hose outside. There shouldn´t be any spill or surge .
TOM