10000 XP, Heavy Pistol
After completing the Full Metal Jacket quest, talk to Titus to start this one. Follow your mini-map to a room with tons of enemies. Use the Meat Bait on the shelf to your left to lure the near a propane tank and shoot it to kill as many as possible. Jump down and use the remaining propane tanks on remaining enemies. Use the propane in the next room to kill enemies also. You will come out by Titus so talk to him for your reward and the Devil's Labyrinth quest.