How do you get a bad smell out of a thermos. It stinks.?

My dad had a trick for his thermos: every day he washed it in soap and water, then after rinsing it he would fill it with warm water and a tablespoon of baking soda and let it stand overnight. The soda removed any film or residue left in the thermos and removed any smells or tastes from the inside. Before filling it back up, he'd rinse it thoroughly. Do this every day. 

Baking soda solution removes odours.

Fill it full of vinegar and leave it closed for a day. Then rinse, fill full of baking soda mixed into water and leave for another day.

Rinse thoroughly and smell again.

If all of these good answers, still leaves a little bit of something that bothers you, then, boil water. Pour it in through a funnel, seal and shake it up good. Pour it all out and while it is still hot, and put in 2 tablespoons of ground roasted coffee beans. Seal and let stand as long as possible before next usage. Rinse that out and sniff a freshness that will even please a 3rd grader.

Us a bottle brush scrubber to get out any built up residue.  I use one on our coffee carafe. It looks like new every time I clean it!

When the thermos is empty..........fill it with Vinegar and warm water.  Let it sit for a while, rinse it out and then wash it as you would with other times you eat on.

Fill it with vinegar overnight and then scrub it good with a bottle brush. 

Remove the dead shrimp

vinegar ?.........

Switch to coffee. Leave some coffee in it for a few days. It will smell like old coffee, but does not affect the taste of coffee. If that doesn't work, then pour some hydrogen peroxide in it. If that doesn't work, buy a second one and let this one air out while you use the other one.

Throw it out .get a new one