The best replacement for airlock is blow off tube.

The best alternatives to airlock are rated as following:
★★★★★  blow off tube
★★★  balloon
★★  cloud nine
★  slime
★  bubbler
★  3 piece
★  blow off
  airlock
  air lock
  blowoff

Your alternative for airlock is not listed? Suggest!
Speaking about airlock, one probably shouldn't forget about rubber stopper.

Other search terms related to airlock and their ratings are:
★★★★★ rubber stopper
★★★★ turbo yeast
★★★★ stopper
★★★ bung
You have in mind a companion for airlock and it is not yet here? Propose!



Google Trends

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airlock
blow off tube
balloon