Urine is hard to clean because it contains organic proteins that bind deep into the individual fibers of some clothing, making it difficult to wash them away.
Pre-treating the clothing is the simplest way to get rid of urine's binding power. Add 4 to 5 tablespoons of baking soda to a tub full of water and swish it around with your hand.
Fully submerge the urine-soaked clothing in the tub for 15 to 30 minutes. Then, drain the water and rinse the clothes in cool water before laundering them