rpt said:
Listening to them is even better.
However, there's no point fitting an airlock if the lid doesn't fit very well. I have two FVs - the 30L is stiffer and has a very well fitting lid. The airlock works nicely. The 25L is much more flexible and although I haven't tried an airlock I don't think the CO2 has much trouble escaping around the lid.
We have an abundance of white tubs at work that look like ideal FVs each come with a sealed lid and locking strap, we have ptfe delivered in them and there's always loads laying around I'm thinking of using them for fermenting, I would say they are approximately 30 litres capacity