There are 4 parts to a bong: Downstem, Bowl, Tube, and Percolator (Tree Perc)/Ice Catcher. There are some bongs that has a diffused downstem instead of the percolator, which is where the bowl pack is attached. The downstems have slits at the bottom where the smoke is filtered through into the water. However, if there is percolators or ice catchers, the smoke will be filtered through there. Finally, the smoke reaches the end of the mouthpiece and ready for you to hit it.