Hi KjAthena...
Protanks aren't carto tanks Kj... but there are some similarities. A Protanks is, what I like to call, a "fancy clearomizer"... a disassembleable, glass tank that uses a coil-head type atomizer.
A "carto tank" is a a disassembleable tank, usually made with a glass or a (citrus juice proof) polypropylene tube, like a Protank at this point, but the big difference is into that tank is inserted a disposable cartomizer.
Cartomizers for use in tanks will have holes in them so that the juice can transfer from the tank to the cartomizer. When the "carto" is worn out after a week or so, you pull it, toss it, and insert a new one. They only cost about $1.10 each and up.
If you go to Baditude's blog page, he's written a good deal on carto tanks, their use, how to prime them and all the variations. I'd suggest you take a look... then go out and get yourself a carto tank, because the flavor is surpassed only by RDAs... without all the "user involvement" associated RDAs. ;-)