In filling the Leo cartomizer you're better off doing it from top down, not the center hole at the bottom. Simply screw the cartomizer on your battery. Then gently, yet firmly, screw the plastic cap off (go in the same direction to screw the carto on the battery). Remove the rubber plug at the top. Remove the carto from the battery. Now with just the carto in your hand, tip it at an angle, and drip your juice choice into the cotton wadding where the cotton meets the side wall of the carto. 3-4 drops, then turn, 3-4 drops, then turn. Wait each time for the juice to soak into the cotton. When all the cotton seems damp or swampy, replace the silicone plug, replace the cap. Wipe any excess off the threaded end with a napkin. Then screw the carto back onto the battery and vape away.