Sorry my phone is being wonky so the reply wasn't working for me. Refilling the Blu Cartos is pretty simple, use a good fork to insert into the hole at the back end (the plastic end) and gently pry until it pops out, its best to try t keep the flavors similar or flavors that would mix well in foods like chocolate with coffee and such. When you buy juice in smaller quantities it will usually have a dropper tip on it simply slowly drip one drop at a time down the inside of the cartomizer in the inside so the fluid soaks the polyfill (the white cottony looking stuff) the trick here is to do this only until the top of this material is wet. You want to wait 5-10 minutes to let it wick into the material and this is why it's best to keep the rubber ends. Refill when the cartos start performing poorly. Try experimenting with different flavors and PG/VG mixes. If you get a gurgle simply blow it out into a paper towel.