![S-Type Airlock](http://winecraftstore.ca/cdn/shop/files/S-TypeAirlock_{width}x.jpg?v=1689105477)
This airlock is the preferred choice for secondary fermenters, as it allows you to monitor the pressure in the fermenter. Fill to line with boiled water or sanitizer to create a closed system, which allows CO2 to escape, but doesn't allow air back in to contaminate your wine or beer.