I never vent intentionally, just incidentally when I'm checking the eggs. I still had to add water to my tubs. I use a vermiculite/perlite blend in sterilite shoe boxes. The boxes really don't seal very well and I usually have to add water sometime during incubation. Most of the problems I've had have to do with the eggs drying out too much. I like that press and seal idea, I think I'll give that a try with some of my tubs this year. One other thing that I do though is to put a paper towel over the top of the eggs to catch any drips that come off the top of the container.