[GTL]

if you think about it, there are two rubber grommets on non-glass on glass joints. the first seals the female downstem to the bong. the second is on the bowl and forms a seal between the bowl and the female downstem. those two frosted glass joints serve the same purpose. the first forms an airtight seal between the female downstem and the bong. the second forms a seal between the bowl and the female piece. you can remove the bowl and the downstem with very little force and they form an airtight seal. they are like the tops to glass perfume bottles.