First make sure you removed the carto filler!! Just checking, but ya never know....
Rinse empty carto tube thoroughly with very hot water to remove all loose and gummy juice.
Shake and blow to pretty much dry out the carto tube as best as you can.
Install empty carto on fresh battery and burn by holding button until cutoff...I usually do this about 5 to 7 times.
After each burn I blow into carto to clear any steam (which normally starts after 2nd or 3rd burn) as well as to aid in drying.
Around 3rd, 4th or 5th burn you will start to see the coil glow red.
Now on subsequent burns you should start to smell a musty burnt smell. All burns prior to this are mostly drying - the smell indicates that you are now working on burning off anything left on the coil.
By about the 7th burn you should see the coil getting red pretty quickly and any smoke will start to be less.
Now that dry burns are complete, re-rinse the carto tube to remove any ash/junk that would still be left in there. Dry well, reinsert dry filler, refill juice and GoGo
DISCLAIMER: If you pop your carto coil doing this, don't blame me. So far I have several times done as many as 10 TOTALLY dry burns one after another with no problem. BUT that doesn't mean it can't happen, and probably will sooner or later. You do this at your own risk, but so far my experience is that the risk is worthy.
Also, the number of burns required will vary on your battery voltage, your cartos level of dryness at the start, as well as how bad the coil is gunked. You'll get a feel for it after doing a few. My experience shows that more than 7 burns leaves you with diminishing returns and likely increased risk, so I usually stop at or before 7...but I have had some that were done after 3 burns, some took more.