Fill to the fill line with sanitizer and insert into a drilled stopper or bung. Clean up and sanitation is easy with the three pieces disassembled. This airlock creates a closed fermentation that allows CO2 to escape from your carboy or bucket but does not allow air back in to contaminate your batch. Airlocks enable CO2 to be released during fermentation, but it traps oxygen from entering the fermenter and harming your beer or wine.