well if I understand how these work and I"m not sure I do, I assume we are basically creating a syphon by sucking through the mouthpiece which is connected to the green tube, this is sucking the liquid in the carto through the coil and up into the green tube. i'm guessing the air vents are connected to the coil part. Not sure why its not leaking through the air holes. I have seen some liquid come out the air holes once or twice, but the thing was gurgling so I can assume it was flooded when that happened.
so I had sat the thing down while typing this and I went to take a puff before I started typing this sentence. it gurgled and liquid came out the vent holes. I unscrewed it off the battery and the battery was flooded as well.
I could see leaving the rubber piece off to stop the syphon on the top, not sure if it would work like that though. or poke a hole in the rubber piece, but then it would probably cause it to leak.