This. If you can’t get the smell out of stainless, you might want to try better cleaning techniques. If it’s the plastic in the lid that’s retaining the smell, look for easy to clean caps. In my experience, Contigo, Zojirushi, and Camelbak have caps that trap odor in the silicone seal rings. I’ve switched to a Humangear CapCap (widely compatible) and removed the two small silicone rings (doesn’t leak without them).