To keep a new flask clean, rinse it with hot water, and let it air dry. If the flask is old and emits an odor, soak it in a diluted solution of bleach or vinegar, and scrub it if needed.Continue Reading
Pour hot water into the flask, swish the water around, and pour the water out. Leave the cap off to let it air dry. It is best not to use soap in the flask to avoid accumulating any residue that may affect the taste of the alcohol.
If your flask has an odor, soak it for 20 minutes in a very diluted bleach solution of 1 tablespoon per gallon of water. Be sure to rinse the flask well with hot water to remove any trace of the bleach.
If the flask is old and corroded, soak it in equal parts hot water and vinegar. Use a bottle brush to scrub it clean.