Ash Catchers are attachments to your bong that catch the ash and keep your bong cleaner. Many ash catchers have percs which can help filter your smoke for a cleaner hit. There are also variants where there are no percs, and these are referred to as "dry" ash catchers. Dry ash catchers will not effect the airflow of your piece or change the function at all, but will simply keep the piece cleaner. When searching for an ash catchers, keep in mind 4 main factors: Joint Size, Joint Gender, Joint Angle, and weight. It is important to have the correct size, gender and angle to have your ash catcher function correctly, and make sure that the ash catcher is not too heavy for your water pipe.