I know clearos have to be cleaned, dry burned, and primed; but what about cartomizer tanks? I heard if they're used, to not let them dry, is that true? How do I store it if it's not in use?
If the tank has juice and the carto is primed and sitting inside, I've had them sit for relatively long times with no adverse outcomes. There's little airflow or change for evaporation, the carto stays wet, and you can just pick it up and resume vaping whenever the urge for that juice strikes you.
If you are talking about pulling the carto from the tank and then using the tank (and another carto) for a different e-liquid? I suppose that if the carto is working and is clearly primed and wet, you could put it into a tiny ziploc, label it, and use it again whenever you choose to refill a tank with that particular juice.
With cartos going for $1-2 a pop, if I have decided that a particular juice is "out of rotation", I will vape until the tank is nearly dry, pull the carto and toss it, clean the tank and either put it aside or fill it will another juice that was "on deck".
The tank itself can be left dry and empty with no harm, the carto (since it was in a tank and has holes/slots) is only going to be effective if it is used in a tank. That's why if the juice wasn't "doing it for me", I just typically toss the carto.