Because of the inside of the flask. If you don't wash it out properly or if you do, the heat of the heats the inside of the flask and you probably drink some plastic with the tea! Just a thought!
If you don't rinse the thermos out right away, bacteria can grow that are truly nasty and taste bad. Also, if you are using dish soap, this can leave a bitter or fragrant residue if you don't wash it all off.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.