An observation, which made me question the use of the three piece or S shaped airlocks. I have a 60 gallon French oak barrel that I love. When I go to top up the barrel after 3 weeks or so and pull the solid silicon bung off the barrel there is a large sucking sound as the evaporated water has created a vacuum in the barrel. This made me think. 1. if I used a three piece or S shaped, add water type of airlock, would that vacuum in the barrel still be there? Would fresh outside oxygen pass the water in the airlock and fill the void? 2. even with the weekly change in temperature of a carboy, does that pushing air out of the water based airlocks and then suck fresh oxygen right back in when it is cooler? I suspect the answer is yes, but it must not be significant. Looking forward to @sour_grapes and other’s thoughts.