筒 (tǒng) is a noun for a rigid, hollow cylinder — like a tube, pipe, or canister — that holds or encloses things. It differs from 管 (guǎn), which as a noun refers to a long, narrow tube (e.g., a pipe or straw) and also serves as a classifier for tube-shaped objects like toothpaste. 缸 (gāng) is a large, open-topped container (jar or vat) for liquids or grains, not a cylinder.