Large mouth canning jar lid for lacto-fermentation (vapor lock). I really liked thecharacterg's version although I didn't want to take up jar space so I mimicked his design a bit. Update (2/20): Alright fellow hobbyists! Well I now have most of the kinks worked out and it is up and running (or sitting). All corrections have been made although I did not get a fill level on it. A rubber band works fine as a seal as well. Printed with PLA at 18% infill (although 15% would probably be fine). There is a lip support in the drawing which will easily break free so no tools should be necessary for removal. I use a rubber band to seal the jar which seems to work just fine. You'll also need to use a canning band to tighten down (I didn't know how to make threads). Just fill it up about halfway with water to complete your airlock and let your recipe sit. Be aware, I'm unsure how to clean it so I just figure to make sure to dry it well after I am finished. Also, maybe try to lightly cover the top to keep dust out of the airlock for long term cleanliness. Anyway, I hope it works well for you all and have a great spring, summer, autumn, & winter!