1 word rice
this is what every smoker should have to clean any piece. 420 Cleaner works like a charm. Literally just squirt a little of that in your bong, add a little bit of warm water and shake for 30secs to 1 minute and your glass is just like brand new, even the SMELL is gone. I mean literally like brand new. No resin scuffs, no smell no nothing. Just about every smoke shop sells it.
Formula 420 Glass cleaner at 1 Percent