Flasks are commonly given away as gifts at weddings and other formal celebrations. Typically made from some type of metal (usually stainless steel and sometimes pewter), flasks are a shiny accessory---if they are kept clean. A common mistake for flask owners is to disregard cleaning the flask, especially if the flask is made from stainless steel. Despite its name, stainless steel can rust and become unsightly. Proper care and maintenance of your flask will help to preserve it.
Empty the flask into your sink. Run the flask under hot water. Fill the flask with hot water and dump it out multiple times. Do not use liquid dish soap; it may stain the stainless steel.
Dip an old toothbrush or dredge pipe cleaners through a mixture of white vinegar and baking soda. Scrub the flask with the toothbrush or pipe cleaners.
Rinse the flask with hot water. Let the flask air dry. Repeat after each use.
Use your flask for its intended purpose: Store only water or alcohol; avoid putting juice, pop or other corrosive or perishable liquids into the flask.