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!
If you swish with hydrogen peroxide everyday you will have the same results plus excellent gum tissue! Recommend swishing with peroxide for minutes morning and night. It kills bacteria that causes decay, gingivitis, periodontal disease. Worth a shot!