Here's what a Joye 510 carto looks like after you crack the plastic base with vise grips and pull it off. Rest of the pictures are terribly blurry, camera's macro feature doesn't work too well.
The plastic shell has a single air vent running up the side to the mouthpiece (you can see it when you pop the 2 black caps off the mouthpiece and look in - it runs all the way down to the atty area), and the cotton wad lives in the filler area. Measured from the metal bottom of the carto, the reservoir is 1 and 3/8 inches long.
This one was completely dry almost when I opened it, no wonder it tasted off. Direct dripping onto the carto's atty worked fine, was able to inhale tasty vapour that way. Perhaps a non-melty plastic tube could be put on the thing for direct dripping, or some kind of wet feed system?
I keep refilling them but they don't seem to wick very well, I end up getting leaks. My kung fu is weak yet..