Is it full on leaking? or are you getting some liquid where the mouthpiece goes in? Plus, I'm pretty sure those tank's tips screw into the tank. I got a couple of those from different manufacturers, and I ended up having random bits of liquid in my mouth from all of them. That was mostly due to either overfilling or getting liquid where the mouthpiece comes into contact with the atomizer. I had one just like yours that would just leak though. The o-ring was still on the mouth piece. It was cheap, and I didn't bother to trouble shoot it. So I just got a cheap polyethylene carto-tank. Oh yeah, GDF!FYPM!