I'm going to admit (with some shame) that over the years, I used just a bit of Clorox in the wash with those white uni pants. About half the amount that I would normally use, and I never had a problem. Of course we didn't have as much problems with clay dirt out here as those of you from my home state of Virginia might have.... wish I had heard about Fels Naptha before now.
(Of course, anyone sporting an Anteater avatar HAS no shame, so please take that into consideration before going the bleach route).