My preferred airlock
I like this style of airlock because it's easier to monitor activity and to tell when you have positive or negative pressure in my fermentor.
This is also nice because it does not allow as much evaporation as a three piece airlock. If you are doing a long term fermentation this is the way to go.
The only reason I can't give a 5-star review is that this things are fragile. I have broken two of them when removing the cap or pulling a stuck one out of a drilled bung.
Reviewed by: Daniel Goniea