Wow, I made it quite a few days without having to ask another tank question! LOL How often should you have to "prime" your tank??? Maybe I am just programmed to feel like the top of the carto has to look slushy at all times that I feel like I constantly have to prime it. After about an hour of vaping, when I pull the drip tip off it looks bone dry on the top.
That's a very individual question. Everything thehangdude said is true. With that in mind, I too have been "programmed" to see a saturated carto from the top, if for no other reason than you can't tell when the dry hit is coming without it. I have a tendency to treat cartos like attys, but I do evidently hit harder and longer than many people.
With tanks, though, it
can be a problem to over-saturate.
Some cartos can flood. Also, tanks basically are acting as a siphon, so the juice will never "naturally" rise in the carto much above the the level in the tank. By the time the tank is half-full, the carto filler 'should' look dry on top even when it is saturated to the level of liquid in the tank. There will be
some wicking, but not a lot do to the self-leveling nature of a siphon.
I have trained myself not to take off the mouthpiece when using a tank. As thd said, it feeds from the bottom--directly into the coil(s)--so you should only have to prime it if you actually get a dry/harsh hit...