I tried to post this in tips and tricks but I couldn't get there. If you try to refill them using the condom method or a syringe you're going to end up with a little more than half a ML to blow out of it. If you hold the carto with a pair of pliers and put the mouthpiece end in boiling water for about 45 seconds the end cap will come right off. You can clean the glue residue off the white end cap with a little lighter fluid and just use a q-tip or twisted paper towel to clean the inside of the cartomizer. Then you can refill it just by dripping juice into the mouthpiece end.