Well, if you're making it yourself, you just use cheap supermarket tea bags--the really basic stuff. Same goes if you're making it with green tea. And then if you want other flavors you add extra things to it, like mint or lemon or fruit.

I don't know how people who make gallon tea do it, but I'd imagine they use about the equivalent, just not in individual bag form. Though their flavors are no doubt flavor syrups.