Dripping a few drops onto an atomizer and
vaping em. Cartomizers/
tanks hold a large amount of a specific liquid, so you can't really "change up flavors" until you empty them out. Atomizers usually get you 3-6 puffs per 2 drops (depending on the resistance/power), so changing flavors is as easy as taking a few drags until the two drops "run out", and then dripping a new flavor right on it.