When you need to clean your bong, and it can be one hell of a job sometimes, use this G-Spot Rubber Stopper to block the joint so you can fill the bong with water and cleaning fluid without spilling it everywhere and making more of a mess than you started with.
They come in three sizes, 18.8mm and 14.5mm for all the three-part bongs, and a slightly smaller, tighter Carb-Stopper that perfectly plugs the carb (rush) hole in a two-piece bong.
So simple, yet so effective. One stopper supplied.