This glitch was patched February 14, 2011 and prior to that there was a very small group of people that knew of it. I'm posting it here for your education and enjoyment.
To take advantage of this glitch you had to begin the While Guthix Sleeps quest. Rather than doing the quest how you are supposed to, once you gained access to the underground Black Knight's base you immediately acquire the Elite Black Knight armor and then go straight to the room with the Dark Squall. Usually you would talk to Silif in the jail cells and realize you needed to go find a key to get him out. In the room with the Dark Squall there is a wardrobe with dagon'hai robes, you would search the wardrobe and get a top, bottom, and hat. After banking the bottom and hat you return to the room wearing Elite Black Knight armor with high alch runes and a fire staff. By dropping the dagon'hai top on the ground and searching the wardrobe you can acquire another dagon'hai top. This method of acquiring tops lasted until you progressed further with the quest. Repeating the process of searching and dropping would leave you with 26 tops on the ground that you could then pick up. You would then exit the room, since high alching isn't allowed inside, and proceed to alch the tops one at a time for 72k each. You made 1872k per inventory. You could then re-enter the room and repeat the steps. The entire process could be carried out flawlessly by a simple bot, producing about 40m per hour. That works out to just under 1B per day if you are constantly abusing the glitch. Again, this glitch no longer works, but hopefully you enjoyed learning about it. I've included some pictures below that verify/show how it worked.
(In the room with the Dark Squall picking up dropped Dagon'hai Tops)
(Outside the room alching tops for 72k each)
To take advantage of this glitch you had to begin the While Guthix Sleeps quest. Rather than doing the quest how you are supposed to, once you gained access to the underground Black Knight's base you immediately acquire the Elite Black Knight armor and then go straight to the room with the Dark Squall. Usually you would talk to Silif in the jail cells and realize you needed to go find a key to get him out. In the room with the Dark Squall there is a wardrobe with dagon'hai robes, you would search the wardrobe and get a top, bottom, and hat. After banking the bottom and hat you return to the room wearing Elite Black Knight armor with high alch runes and a fire staff. By dropping the dagon'hai top on the ground and searching the wardrobe you can acquire another dagon'hai top. This method of acquiring tops lasted until you progressed further with the quest. Repeating the process of searching and dropping would leave you with 26 tops on the ground that you could then pick up. You would then exit the room, since high alching isn't allowed inside, and proceed to alch the tops one at a time for 72k each. You made 1872k per inventory. You could then re-enter the room and repeat the steps. The entire process could be carried out flawlessly by a simple bot, producing about 40m per hour. That works out to just under 1B per day if you are constantly abusing the glitch. Again, this glitch no longer works, but hopefully you enjoyed learning about it. I've included some pictures below that verify/show how it worked.
(In the room with the Dark Squall picking up dropped Dagon'hai Tops)
(Outside the room alching tops for 72k each)
