I'm trying to make my own bubbly water but I don't have a keg. I wanted a small one (about 1 gallon) to fit in my fridge but they only sell larger ones. So I bought a gallon sized thermos. It looked pretty well-sealed and was advertised as keeping cool temperature for hours. So I attached a ball lock keg coupler to the screw cap and started pumping co2. Problem is the entire lid pops off at around 30psi (even though it screws on)

Anyways, I am wondering if there is some way to seal the top part of this large stainless steel jug. It doesn't really have a lip so it's tricky. I might just buy a different container if there are no solutions.