To remove persistent stains from white clothing, I mix one part dishwashing soap and one part white distilled vinegar in a small medicine cup. I dab this mixture on the stain and let it sit overnight. The stain usually fades completely by morning, but if it hasn’t, I rub more of the mixture on the spot and let it soak in again before washing in cold water.
It’s a safe and effective chlorine bleach alternative, and it works with many fabrics, although I would recommend testing the fabric before treating the whole garment. My homemade stain remover has been effective against red fruit juice that spilled onto a white sweater and sweat stains under the arms of white cotton shirts.