If the shirts are white try soaking them in a solution of 50% bleach and 50% water. You can add a little laundry detergent to the water if you want. Check it after 30 minutes, if the stain is fading then let it sit a little longer. When the stain has faded, wash the shirt as usual. If the shirts are colors, soak them with Oxyclean. Get the powdered form of Oxyclean and follow the directions on the package.
If you put the garment or cloth into a pot of water with 3 or so scoops of powdered BIZ and boil under a watchful eye, the stain should eventually come out. It's fine for antique cotton cloths.
You tAke the spot and put like a ruber band around it and tie it tight the you let the spot sit in some bleach