The Dry Trap Airlock is a step forward in Airlock technology. While most airlocks rely on a water barrier to keep oxygen from your beer, the Dry Trap Airlock utilizes a solid seal between a glass ball, and a precision molded PET seat. This means that your airlock can't go dry, there's no water to suck back into your beer due to temperature change, and it will not let ANY oxygen into your aging beer! The Dry Trap Airlock is designed to work in conjunction with the PET O-Ring Closure, and is specifically for Better Bottle Plastic Carboys. You will need to purchase these other items separately.