Most of you may know this, I did not until recently, so thought I would post for everyone just in case.

When you first enter Hellfire Ramparts there is cliff to the right, its what you can jump down after beating the final boss for quick path back to the entrance.

Park your slaves at the entrance (far enough from your spot they wont aggro), then run your tank all the way through while aggroing everything and jump down this path. Then sit and wait because soon a million mobs will be running towards the entrance.

Its a very very quick dungeon.