I see a lot of people asking online about preventing evaporation, with lot of suggestions ranging from expensive polystyrene balls, custom cut cambro tank lids to just “keeping the water topped up”. I just thought I’d post my method, which only uses plastic wrap, so it’s probably the easiest and most accessible but also very effective. We often cook for 36 hours like this and never had to top up water or had evaporation / condensation problems. I imagine it also traps some heat to save a little power too.
First, fill your tank / pot / etc do the required level depending on your circulator. Add your bagged food so you know the level is correct before you seal it up.
Then, seal the entire container with plastic wrap, overlapping a few times so that it’s fitted firmly and down the sides enough that it won’t slip later. I find three layers is adequate.
Cut a small hole that barely fits your circulator. Hold it’s base against the plastic till you can judge it by eye. Be careful not to slice into any bags.
Turn it on and start your cook. It’s also handy to write the time / temp on the plastic if it helps you remember when to take it off.