How can I remove feces stains from rubber and vinyl adult incontinent pants?

Yep. Ditch the rubber and vinyl and get disposables.

Exactly.

When in doubt, throw them out. Buy disposables.

I personally wouldn't want to use these, I imagine they would be incredibly uncomfortable. However, vinyl and rubber are notorious for retaining odors, I doubt even bleach would help. As for the stains, they ARE incontinence products, there is such a thing as being too fussy.