I can refill cartos 10-20 times before they need cleaning...and it's best to use the same or similar juice. I use them until they just don't draw right or taste gunky.
I have about 100 cartos between my wife and I...and we have a baggie where we put cartos that need cleaning. Every couple of months, I will have 50 or so that need cleaning. This works well for me, takes about 30 minutes, and I have only tossed 2 or 3 cartos in 8 months.
1. Remove end piece and soak cartos in everclear or vodka overnight.
2. Rinse in strainer with very hot tap water.
3. Boil for about 5 min.
4. Rinse with hot tap water and repeat boiling.
5. Rinse and repeat 3 or 4 times until water is clear and oderless.
6. Bake at 175-200 degrees on cookie tray for approx 1 hour.
7. Turn off oven and allow cartos to cool in the oven.
8. I let them continue to dry for several days...but I have enough cartos to do this.