First, take the body of the vacuum flask, wash it thoroughly, and wipe it dry. Be careful not to use detergents with strong or pungent odors, as this may negatively affect the flask's performance.
Remove the lid, detach the sealing ring from it, then rinse both the lid and the ring with clean water and wipe them dry.
Place the sealing ring onto the raised ridge of the lid, and press down firmly to ensure it fits snugly and completely.
Place the lid onto the flask and twist it firmly until it is securely tightened.
Water-tightness Test: Invert the flask, fill it with water, and then gently shake it a few times to check for any leaking water droplets. If any leakage occurs, you must re-install the lid and sealing ring until the flask is completely leak-proof.