How to clean your thermos

I always take my thermos to work, either put hot soup, coffee or other liquids in it. And after a while the thermos smells and it is hard to clean. After a few experiments I found this to be working.
Take some vinegar, pour it in a pot and bring to a boil. As soon as the vinegar boils, pour it into the thermos right away, close it and put the thermos upside down. Most of the dirt and smells are right at the top so this way all of that will be broken off with the vinegar.
Let it sit over night, then the next morning clean the thermos with some dish detergent and rinse out. The thermos should be very clean after that and the bad smells are gone as well.