A small drilled bung that will fit into the tubing will work, also. I clip mine to the handle of the fermented so the airlock remains upright and functional. I so rarely do this, as I pressure ferment, typically, but I had a Dry Stout that I made a couple weekends ago and when fermentation was slowing, I installed the airlock in this manner. The batch will be racked tonight, if time allows and the system will be lined up to another piece of tubing going to a CO2 purged cornie for filling with low O2 ingress in the system and a Co2 purged line to the ball valve for liquid to the keg...this works like a champ for a closed loop system.