Funny, we are using these in our lab for a project totally unrelated to fermentation. We are using them to provide controlled humidity environments over saturated salt solutions. They appear to seal very well in that applications. I'll second @Hoppy2bmerry with the airlock method. I use a similar set up for rice wine.
I am using something similar, mine are Bormioli Fido 5L jars, originally intended for storing dried foods. Drilled the glass tops with a 12mm diamond coated bit for the airlock grommet.