I have successfully cleaned about 25 cartos with the boiling water/baking for 90min system, with some of them on their 2nd cleaning. Only a couple completely failed after this, and the ones previously filled with a strong cinnamon (Freedomsmoke Fireball) retained some of the old flavor.
1. Remove the caps
2. Place them in a bowl
3. Pour in boiling water from a kettle
4. Agitate with a slotted spoon
5. Pour out the water, and repeat steps 3 and 4, up to 3 times
6. After pouring out the water for the last time, shake the excess water out of each carto.
7. Place cartos on clean cookie sheet
8. Bake in oven at 250 F for an hour to 90 minutes, more if you have a lot of them.
9. Turn off heat and allow to sit in cooling oven overnight
I fill them the next day. Works like a champ.
Cheers,
Otto