Dissolve a couple of Alka Seltzer tablets in warm water. Use a bowl large enough to fit the shirt and pop it in for 15-20 minutes. Or, cover the stained area with white vinegar, rub it in, apply 1/4 part water, 3/4 part baking soda directly to the stain. Wait a few hours or overnight. Wash as usual but add an extra 1/2 cup of baking soda.