S-Shape Airlock (aka Twin Bubble Airlock)- PLEASE SELECT THE QUANTITY. These plastic airlocks are the industry standard for home brewing. Fill the airlock to the fill line with sanitizer solution and then plug into a stopper or grommet in order to form a tight seal! Please do not hesitate to ask any other questions! A happy customer is our goal and as such we will get back to you immediately with answers to your questions. Please note that some items may not be combined.