When you ask yourself, "What's the best way to clean my bong?" you really have two very amicable solutions..one is a little cheaper than the other but were gonna explore both options
Tea Tree oil & hot water - By using about a 1-1.5 tablespoon (depending on the size of your piece) and hot water combine the two and swish thoroughly. Caked matter will start to dissolve and liquefy into the water. After about 80% has resolved . Repeat this process. After Ensured Drying and approx 3-4 hours the vent (smell of the tea tree oil is quite potent) You should be clean as a whistle!
Isopropyl Alcohol and Coarse Salt - (this method may finely damage some glass types) This is definitely the cheap route to go. But with a little bit more patience and vigorous shaking the solution is about 90% the same. With about 4-5 tablespoons of salt and an entire bottle of isopropyl, Contain your item within a bag and fill the piece with salt and iso alcohol. After some light shaking leave the item submerged over night and rinse thoroughly after 8 hours. Repeat Process if necessary.
We hope this helps with your piece!