How to get Garlic & other strong Spices' smell out of my Zojirushi Flask/ Thermos acquired via a herbal Immunity decoction?
Wash out with warm soapy water. A toothbrush could help in the scrubbing. While still wet, add baking soda into the flask and scrub. 
Pour an inch or two of white vinegar into a clean carafe, then fill most of the way with hot tap water.
Not tried this one, but seems a few people have had good results. 4 Alka-Seltzer tablets with water. 
Adding freshly ground coffee, which will help to mask the smell if it is still there. 


Edit: 
Just read through the manufacturer's instructions, and have updated my advice as a result.