tight as a drum
Taut or close-fitting; also, watertight. For example, That baby's eaten so much that the skin on his belly is tight as a drum, or You needn't worry about leaks; this tent is tight as a drum. Originally this expression alluded to the skin of a drumhead, which is tightly stretched, and in the mid-1800s was transferred to other kinds of tautness. Later, however, it sometimes referred to a drum-shaped container, such as an oil drum, which had to be well sealed to prevent leaks, and the expression then signified "watertight."
Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.