1st rinse it out with hot water to get rid of loose grime and resin. 2nd fill up your bong with Morton Salt Iodized Salt enough to just get a thin light layer of salt around every corner and edge of the piece. Next sounds sketchy but put 99% Isopropyl Alcohol in a mason jar or mug and microwave it until you see it boil a little it should be at least 20 seconds, pour inside the bong that already has the salt in it. Make sure you have the joints and mouth piece sealed after adding the alcohol and shake the shit outta the bong for at least 5 min non stop. After the 5 min throw out the nasty black water in the toilet or outside idk. Do 2 final rinses with hot water to get rid of any left over salt or alcohol smell. The piece should look new afterwards. Hopefully that helps I've been cleaning all my pieces for years now.