Downstem is essential for bong operation and is much more basic than percolators in function and appearance. A downstem is a diminutive and removable glass piece that houses ground cannabis. In this the tube is inserted into the main water chamber which allows air to enter the chamber to improve the air flow and cool the vapor.
Descending stems are a common feature of water pipes. They can be easily removed and cleaned, and replaced with different bottom rods if necessary. However, make sure that the descending rod is the correct size.