Down stems in a bowl of water pipe/bong, the down stem connects the bowl to the water pipe/bong or body. It does function as the smoker inhales through the mouthpiece which creates suction that pulls the smoke through the down stem section into the water pipe or bong and then to the user.
With a water pipe/bong or bubbler, the down stem connects the bowl filled with herbs to the water-filled reservoir. As the smoke is pulled from the herb into the bowl, down through the down stem, and then into the bong water, it is cooled and creates a smoother, cleaner hit.
