Originally Posted by Carbon
If I were doing this to my drum I'd use what I already have on hand, tool wise, and probably do this:
I would first trace an outline on the drum around the 1.5" nipple. Then I would drill a 3/4" hole in the middle. Then I would make multiple straight cuts with a zigsaw from the hole up to the outline like slicing a pie. I would then completely bend each tab back into the drum to form a round hole. The more slices you make and bend back the cleaner the hole will look.
i like that.. just have to make sure the nipple is long enought to have thread outside for the elbow and inside for a locknut