rogueraven wrote: For Helenchild, Have you tried baking soda + white vinegar? My boyfriend can never seem to keep track of his many thermos bottles, with creamer and sugar in them. This has been the best fix I've used of late. Pour baking soda in thermos (1/4 cup? or so) then pour in white vinegar (1/2 cup). MAKE SURE YOU DO THIS IN A SINK AND AT ARMS LENGTH. The chemical reaction is fast, kind of boils/foams. My first time , I used way more than needed, was a large Stanley and had to mop up a mess. When this stops I put the thermos aside over night, sometimes it has taken more than once but has worked to get that gunk out and stain too. Just realize this combo is what we used to fuel our toy rockets when we were kids. WARNING: Do not put any lid on a container, or it may look like those pranks the kids are doing these days with Mentos candy in a plastic soda bottle - They violenty explode!
Second photo is silly, but keeps me trying at things with a smile.