I bought some Tupperware cereal containers online. It was from the goodwill. They put one container inside the other. They were the same size. How do i separate them without breaking it?
Try putting them in hot water for a few minutes and see if that helps.
I would not use old Tupperware especially for liquids. Most were made before the dangerous things were removed from them. I don't even store liquids in new plastics. I do use plastic for solid foods.