I used my stainless steel Hydroflask to make coffee when I camped. It worked great btw. It was designated as my coffee "pot" and never used for anything else. It reeked of coffee and stained with coffee.
I wanted to use something else for camp coffee and clean my Hydroflask. I tried many things but nothing worked. Finally I went to you tube. I found videos of folks using dishwasher pods.
I gave one a try and OMG it worked. Even the smell is gone. I can use my Hydroflask for water now.
Directions I used were, add pod to cup then add hot water ( I used water from a tea kettle ). Let stand for an hour or two. Pour out water and wash out.
It was really awesome it worked and now I have my cup back.