Don't you get juice in your mouth? Especially if it's in the center tube?
Not at all. Remember, you have to keep the battery-end condom (the one with the nub inside) on while filling/sucking. When you suck, it creates a vacuum in the cartomizer, moving the air into your mouth and the juice into the filler. When the juice is pooled on top, obviously there will be some in the center tube, but I usually just see air bubbles rising up from it. After you suck and displace the air, the center tube is automatically cleared out, as all the juice has gone into the filler.