Glass bubblers are often fancifully designed with long, winding necks and curved edges. Because they're usually made from one piece of glass there is often no way to remove any parts, making them difficult to clean. Tobacco resin often builds up in the nooks and crannies of bubblers, making it especially hard to reach. Disposable pipe cleaners are the most helpful tool and are inexpensive.
Fill a Ziploc bag about halfway with rubbing alcohol.
Fill the bubbler with rubbing alcohol, place it in the Ziploc, and let it soak overnight. This will help loosen deposits of resin.
Remove the bubbler and let the liquid drain.
Add fresh rubbing alcohol to the bubbler as well as a small handful of bath salts.
Plug the holes in the bowl and carb with your fingers and shake as hard as you can.
Let the liquid drain and use a pipe cleaner to clean crevices inside the bubbler.
Repeat steps 4, 5 and 6 until the inside of the bubbler looks clean.
Rinse the bubbler with hot water when you're finished.