What's wrong with the old bottle stopper?
If the containers are of good quality, use a heavy lid. Otherwise, wait for the water to run and put the lid on.
Here we should popularize the knowledge of atmospheric pressure. When the hot water into the thermos bottle, the water is hot, intense activity of water molecules, water molecules for gas is very active at this time, the bottle cap, the bottle at this time pressure than the pressure outside the bottle was much higher, because the cork jumped out.
