This food grade silicone rubber O ring is custom-designed to slip into the plastic lid on Siphonless Fermenter sold before 2020. This does not fit our latest Siphonless Fermenter, sold from December 2020 and on.
This will provide an airtight seal so the airlock bubbles even during the least vigorous fermentations.
This food grade O ring fits in loosely, and can easily be removed for cleaning. This is not required for a successful ferment (beer will not spoil if you do not use this O ring), although it is recommended for those who use the airlock as a primary fermentation indicator.