Empty out your flask if there is any liquid in it. Load the flask about a quarter of the way full with ice. It’s best if the ice is crushed or in smaller, irregularly shaped pieces, though normal cubes will also work. The exact amount of ice you use will depend on the size of your flask.  The type of bagged ice you can buy at the grocery store is perfect for this task. If you only have access to large, smooth or rounded ice cubes, you can break them up into a more effective size yourself by placing them in a plastic bag and crushing them or throwing them in a food processor. Sprinkle 2-3 heaping spoonfuls of salt over the ice. For the purpose of cleaning, salt of a larger grain, such as coarse-ground kosher salt or sea salt, will get the most done. Add the salt to the flask quickly so that the ice you put inside doesn’t have a chance to melt.  Use an extra half tablespoon (about 7ml) of salt if its a finer grain. Ice that melts in the flask may dissolve the salt, making it less useful for cleaning. Place the lid on the flask and make sure it’s secure. Shake the flask vigorously. As the hard ice and jagged salt granules move around inside the flask, they’ll scrape away whatever stains and grime have accumulate on the insulated metal. Shake for as long as you want, until you feel confident that the ice and salt have done their job.  The salt and ice combination will essentially act as an “exfoliant” for the walls of the flask. Don’t worry about damaging the metal that your flask is made of. They’re designed to withstand extreme temperatures, mild impacts from being dropped and general wear and tear. Take the lid off the flask and pour out the ice-salt mixture. Run some warm water into the flask and swirl it around to remove any lingering remnants. Rinse the mouth of the flask as well, and leave the lid off as it dries. Using ice and salt to wear down stains is a safe, natural solution. Both ingredients are non-toxic and don’t contain chemicals that may be harmful if ingested.
املأ القارورة بالثلج. أضف بضع ملاعق من الملح. غطِ القارورة ثم رجها جيدًا. اشطف القارورة جيدًا.