The Fumo stainless steel hose one-way valve fitting is an optional accessory that can replace either the all glass or stainless steel regular hose insert fittings. You would want to use this fitting when you have multiple hoses being used on a single hookah. It eliminates the need to block the mouthpiece opening while other users are drawing air through their hose. The way the valve works is that it allows airflow to be drawn in from the hookah pipe but the flow cannot be reversed back into the hookah. The fitting consists of three separate pieces that can be easily disassembled for easy cleaning after each use. It's all stainless steel construction makes it durable in the most demanding environments.