I cleaned my njoy atomizer today with Polident made for retainers and partials. Package said it cleans tough stains and is safe for use on metal. I used about 1/2 cup of hot tap water and soaked the atomizer for 5 minutes. Then I took it out leaving the atomizer about half full with the solution and gave it a gentle shake with fingers over both ends for maybe 30 seconds. Then I rinsed it well with tap water. Next I blew my brains out on the battery end until no more water came out. I dried the outside with a towel and then used a cotton swab to really dry the outside end that connects to the battery. I also swabed the inside of the tube being careful not to touch the little bump at the bottom. Then I dripped 3 drops of e-liquid in the atomizer, popped in a cartridge and began puffing. Works like a charm. This atomizer is a month old and smoke production had decreased somewhat. Also, I tried using Crown7 cartridges in my Njoy and after a couple of puffs, it tasted burnt. There is still a hint of the burnt taste, maybe from some fibers getting down in the atomizer. But it's a lot better. Won't be using anymore Crown7 cartridges. Probably will end up squeezing out the liquid from these cartridges and using it to refresh Njoy cartridges. Next thing that would make sense to me would be to gently scrape the little guts of the atomizer and then use canned air to blow out any debris. But that's for another day. 
