I'm finally getting the complete hang of filling/refilling cartos. I now have 6 of them going at once and are working perfectly. Using the syringe method for initial fill, then topping off with the dropper. I now know just "how much" to add visually. I also take a paper towel by rolling an end, swabbing any additional juice that remains on the inside of the carto before putting the cap back on...PERFECTION! 