Try this recipe for removing tough yellow stains on your special whites!
1. Mix 1 tbsp of regular detergent, 2 tbsp of hydrogen peroxide and 2 tsp baking soda.
2. Apply the mixture to the yellow stain and scrub gently.
3. Leave it for two hours.
4. Perform regular wash, and pour one cup of vinegar when rinsing. (Urine contains luna ammonia, and can trap detergent. Vinegar neutralizes detergent and washes out the ammonia.)
It's a near-guarantee of bright & clean!