Although I didn’t test the statement directly, I have every reason to believe it is a valid conclusion, based on my observations. When the dry ice was in the cooler, I could feel cold “air” leaking out of the closed drainage valve. I know the CO2 was sublimating and expanding, causing an overpressure in the cooler. I know that CO2 is heavier than air and without mixing would sink to the lowest point. Therefore, this was most likely CO2 leaking out of the valve. It was a surprising amount, like the feeling of holding your hand in front of your mouth and blowing gently.
If the drain valve was closed, You were not feeling co2 leaking..
It was simple cold to warm air convection.
co2 can mess your foods taste up. You should have the coo2 contained away from the food and a vent of it's own..
I would use a metal (xmas) cookie tin with a brass tube feeding outside the food cooler.. Put the tin in cardboard to protect your hands..
Butt that's more work than I'm in for.. BM is a camping trip.. Throw some ice in a cooler and stop screwing around..