Cartomizers and cartotanks have a learning curve, but if you follow a proven method you should be up and vaping in no time.
You learn quickly.

The one problem with the metal cartomizers is that you can not view the juice level, so you risk vaping it dry unless you frequently top it off with more juice. Once a cartomizer's filler has becomed burned from a lack of liquid, you'll never get rid of that taste. You'll have to discard of it and start with another.
If you put a "punched" (holes) cartomizer in a cartotank, you can view the juice level easily to know when to refill the tank (before the level goes below the carto holes). The tank naturally feeds the carto as you vape. You should be able to get approximately 30 ml of juice through a cartomizer before the draw becomes tight and then need to be replaced in the tank.
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The juice remaining in the tank can be saved when you decide to change out cartos. I strongly suggest that you
get a tank tool like the Slap Yo Moma tool to make this process faster and easier. The tool also saves your tank's o-rings from unnecessary wear and tear. Well worth a purchasing investment. It comes as a stainless steel tool or a less expensive delrin plastic option; both work equally well.
Slap Yo' Mama Adapter : Big Daddy Vapor
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I use a different method of filling a cartomizer and tank than The Ocelot uses. No one way is best or better, only the one that works best for you. Try her method and my method and see which one you prefer. I use a wood toothpick to plug the center air hole of the carto, therefore no juice gets in there that you have to blow out or taste.
http://www.e-cigarette-forum.com/forum/blogs/baditude/3710-5-cartomizer-tank-setup.html