In Zul'drak you get a quest to douse house fires (Both horde and ally).
If you are a priest and you have the talent Improved Spirit Tap you can get spirit tap easy.
You get a quest item with a cooldown of less than a second.
Go around and spam that bottle and sometimes the water will critical hit. Thus giving you the spirit tap buff.
Use this to gain mana whenever you are doing the quests there.
You can use the bottle even after you have 15/15 houses doused.