Carboy Ventilation Bung
The silicone breathing bung can function as an airlock for extended aging of beer and wine. Made of natural white silicone, the bung has vent holes through the center, and a silicone flapper that fits tightly against the holes. This allows gasses to escape by pushing up against the flapper, and then the valve shuts protecting the product from contamination.
#7 breathing bung is recommended for use in glass carboys.