Try OxyClean powder or spray. I got mustard out of my daughter's shirt by soaking it in Oxyclean for 30 minutes, and adding more of the powder when I washed that load of clothes.
Have you tried soaking in dish washer detergent and warm water? If you haven't, try 1/4 cup detergent in a bucket of water. Make sure the clothes are covered in the solution. Soak for 2 days, then pour into your washer and wash as usual. You may want to try one piece first to see if it works as well for you as it has for me.
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