well seeing as people spend hundreds of dollars on serious valve cover ventilation to evacuate as much crank case as possible, i'd have to go with air only going out of the tubes

and the wonder of a PCV valve is that its a one way device, and i've have mine crap out and it blew out my dipstick, indicating pressure

but just put your finger over the hole, or take your oil fill off for a second and put your hand over it