C.V.
Fels Naptha.
It's a big bar of soap found in the laundry aisle. Works better than any stain treatment out there.
Just wet the garment and rub the bar into the spot until you've worked a good amount of soap in. Let it hang out a little while and launder as usual.
It also gets out blood, juice, and lots of stains that you'd think were already set in. Works fabulous for ring-around-the-collar on white shirts, and get sweat stains out too.