This quest functions differently from most others in that when you complete it, your group zones to a different instance to loot the chest. These chests contain some very top-end named items as well as Tome pieces that you collect for some of the current best loot in the game.
This exploit works about 90% of the time. Take your group through the quest like normal, but when you finish the named encounter at the end, everyone stay inside except the group leader. He zones out to the other instance and loots the end-reward chest. Then have the leader run back around and re-enter the quest. Once he's back in, the rest of the group zones out to get the chest, then return to the Necropolis. Disband the group and have the group leader (who is still in the quest) reinvite everyone. This will reset the instance that has the chest in it, so you can loot it again without having to complete the quest at all.
So here are the steps
1) Complete any of the Pre-Raid encounters in the Black Mausoleum (Vol and Cinnis are easiest)
2) Group leader zones out to orchard and loots chest
3) Group leader runs back through Necropolis and re-enters quest
4) Remainder of group zones out to the orchard and loots chest
5) Remainder of group runs back into Necropolis and disbands to reset Orchard instance
6) Group leader re-invites everyone
7) Everyone zone backs into the Black Mausoleum and does a MOB free run down to the Orchard entrance
Repeat from step 2
Sometimes the black barrier at the very beginning of the quest will drop down and you will be unable to run back down through without resetting it. I'm not sure why this happens yet, but it only happens about 1 / 10 runs.
This is a great way to collect some very nice gear and the highly valued Tome pieces.