Try soaking in 50 % bleach water.
I can tell you that I have used bleach and water in my stainless steel sink without a problem. But you may want to try a test item yourself.
Here are some other ways to clean up stainless steel. They start with natural materials and move forward from that. One of these ideas might help. There is also a section about the chemistry of stainless steel. Wishing you the best.
Hi Don: You can try pouring a little white vinegar or apple cider vinegar onto the stained surface. Let it sit for a few minutes; the gentle acid in the vinegar may lift out the stains. Rub the stained with a soft cloth, following the grain of the steel. Rinse thoroughly, and dry the surface with a clean towel. Or:
Apply a mixture of baking soda and liquid dish soap, the consistency of toothpaste, to a microfiber cloth or another soft cloth, or you can try using a magic eraser. Then rub the stain, moving back and forth in the same directions as the grain in the metal, not in a circle. After scrubbing, rinse the stainless steel surface thoroughly, and towel it dry.
That should do it. Good luck