The instructions for these things literally say to not ever clean them. Well, I'm not exactly one to follow all instructions.
I end up fully disassembling mine every couple or few weeks, to thoroughly clean the ceramic insulator and electrodes with rubbing alcohol, cotton swabs, and even a toothbrush.
Note: Remove the ceramic insulator from the device before attempting to clean it this way, as practically everyone should know already, rubbing alcohol is flammable..
Better yet, just have an experienced electronics tech do it for you if you're not 100% sure how to fully clean it yourself.