Glass dry/ash catcher by Phoenix Glass helps prevent any rogue ash from entering into your main piece.  Light weight with a flat base it can be left on your rig or stand alone on a flat surface.  Small enough to put onto most waterpipes and big enough to catch a sesh worth of ash without the need to clean in between.  The design does not water filter the smoke at all, the piece only serves to stop the ash from entering your main piece.