Looks to be standard airline tubing, maybe a tab smaller.
But, I don't use the bag anymore... I sealed the bottom of the chiller with silicone, and I just pour the food in. I've been leaving the top off too, with a stirring stick there, and stir it when I think about it. If you mix the right amount of the Sodium Alginate powder with the home-blendid oysters, it will stay mixed and not need stirring for a week or two.