The packs right before the last boss in mechanar will keep spawning and not get you out of combat, this could cause mana problems for the healers. We used a priest to MC one of the mobs that spawn, if you kill the others and let the MC-ed mob MC-ed, you will leave combat and will be able to drink.
I have not tried if the MC-ing priest could drink, but I could at my shaman.
So basically:
-MC one of the mobs
-Finish off the other ones of the pack
-Leave combat
-Start drinking
-Nuke the last mob and continue killing the packs
This works with any pack as long as they and MC-able.