Think he's talking about the cover/sleeve that goes over the actual battery.
He may be talking about the metal cone itself.
As stated above I clean out the threads and battery connections with a Q-Tip/old sock/paper towel and rubbing alcohol. The atomizer itself I never really clean, they are cheap enough to just buy a new one, how ever if you must, just rinse it in some warm water for 20-30 seconds and let it dry completely. The rest of it, the cone and the base connection itself, including the plastic mouth piece (it can get kinda gross from being in your pocket), I just wash in warm soapy water and rinse thoroughly. However, never use rubbing alcohol on the base connection for the atomizer housing, the one that screws on to the battery. I used to do this and they were constantly going out, and I realized there is a little rubber seal in there and the alcohol eats away at it. Good luck.