I had to use this in anger the other day: sudden sore throat after one harsh rip and no time to change mouthpieces.
Imagine my surprise and delight to see i) hydrotube with fresh water in reach, and ii) this o-ring sitting on my AVS mouthpiece. I like that the o-ring doesn't get in the way, it just sits there quietly until needed. At this price I would be happy to have it, and never use it. Thanks for sourcing these for us RecVapes.