The ego-T is a tank system, hence the "T", but different than what most users here would call a Tank (ie. j-tank or DCTank). The ego tank is a 2ml plastic container that sits on top of a propriety atomizer from joyetech (the makers of the ego systems). There is a newer version called the "C" which is easier to maintain but is still rolling out production and doesn't have all the options available yet. You can find "t" kits at a lot of vendor sites such as
Cignot ®
I have used the ego-t & c in my second stage of vaping gear (started on the slim-style batteries). I can say that in terms of vaping convenience it's very easy to use. There are some maintenance issues that you would need to learn about. The down-side in my experience, other than the maintenance issues, is that it is a little light on the flavor and you occasionally can get a plastic-taste. Whether or not you decide to get the complete ego-t tank system, i can highly recommend the ego batteries on their own (again, sold separately or with the t & c kits). They do work very well with many of the other options available such as regular cartos, mega dual-coil cartos, DCtanks and such.
i have since moved on to another system but still use the ego batteries from my original kit when i am vaping out of the house.
sorry rambling, to answer your question - you can reuse ego tanks. in the kit you get 5 tanks. only reason to buy more would be if you wanted to keep more flavors in them simultaneously.