@spent2much - My go-to's are Dawn dishwashing detergent- the original blue one, and scrubbing with Ivory soap. I work the Dawn in the material with cold water, let it sit 15 minutes, then wash with cold water. One of these usually works when I don't know what a stain is!
Whenever you have a stubborn stain on something and find you need to try some other stain remover, the key thing to remember is DO NOT put them in the dryer to dry them until you're positive the stain is gone.
Drying the garment will "bake in" the stain and it will never go away. I've tried many times and now know better.
Have you put these white pants in the dryer? It might affect what others suggest.