The term 'not watertight' can be described by two crossword solutions: 'LEAKY' (5 letters) and 'POROUS' (6 letters). LEAKY is an adjective that means allowing liquid or gas to pass through a hole or crack, while POROUS is an adjective that describes something that has many small holes or passages that allow liquids or gases to pass through. Both words describe something that is not watertight, meaning that it does not prevent the passage of water or other liquids.