I started off getting extra juice and am already mixing my own (take care with that, make sure to READ in the forums!). You can get plenty of premixed juice (hit up the juice review section for more info) and if you check out the modders section you will find plenty of info on re-using the carts. I just pull out the stuffing, rinse well, lay it on a dry cloth and dry. Refill with clean juice

There are several things you can restuff them with, I tried the teabag mod and it worked OK, then I used the poly stuffing (I had some laying around since we have a big fishtank) and that works great. Best yet? Simple slices of Fluval, the fluffy envelopes you put charcoal in for fishtanks (thanks Mary Kay!!!). That is clean, easy, and lasts a long time with the rinse/dry/fill method!