Screw-on bubbler

I like to brew my own non-gaseous drinks, specifically mead. This generates a LOT of CO2 gases, and you can't let it ferment to open-air either.

This is where you need a bubbler to act as a gaseous valve. In this particular instance, just screw it on your bottle top (I'm using cleaned soda bottles), fill the top with water up to below the inside gap, and voila!