One part Dawn dishwashing liquid mixed with two parts HYDROGEN PEROXIDE. Add baking soda for scrubbing help. Use laundry brush to work into the stain. Supposed to actually take yellow armpit stains out of white shirts!
Hard water stains: DIY Shower Cleaner 24 ounces of water cup hydrogen peroxide cup rubbing alcohol 2 tsp dishwashing liquid (original recipe calls for Dawn. I use whatever I have on hand) 2 tsp automatic dishwasher rinse