Stainless steel Thermos flasks have become an indispensable part of modern life. They keep our coffee hot while we're on the go, keep our children's juice fresh at school, tote lemonade to the beach in summer and keep hot chocolate warm during Christmas tree hunting expeditions. With all the use they see, they can get pretty grungy and occasionally harbour the odours of eggnogs past. Regular cleanings will keep your Thermos looking and smelling fresh and ensure that your little angel's fruit punch doesn't taste like stale coffee.
Discard any liquid left in your Thermos and give it a quick rinse, pouring the water out of the opening from which you usually drink. Disassemble your Thermos flask, removing the top and any other removable parts on your model.
Wash the body of the Thermos inside and out with a wet washcloth and a dab of dishwashing detergent, and rinse well. Never immerse the insulated part of the Thermos in water or put it in the dishwasher--water could seep in through the seams and ruin the Thermos. Avoid using abrasive pads or cleansers that could dull the stainless steel finish.
Wash the Thermos lid with hot water and dishwashing detergent, using a nipple brush to get gunk out of the crevices. If there is a lot of build-up on the lid, allow it to soak in hot, soapy water.
Remove odours and lingering tastes by washing the flask and lid with vinegar, then washing them again with soap and water. Scrubbing the inside of the flash gently with damp baking soda is an even more effective way to remove lingering smells and tastes, but doing so can dull the stainless steel finish.