The 4.0 Drycatcher is a work horse. The design makes the ash to go to the bottom, while allowing maximum airflow to move through the piece. It does this by having a stem with 8 slits and an open bottom
It also features a tortured path of impression on the glass. This makes it harder for the ash to move around plus reducing the volume of the Drycatcher.
The main purpose of these are to making daily cleaning of your tubes easier. Especially on fixed stem tubes that can be a real chore to clean.