In order to remove urine stains from your spandex leggings, you should immediately flush it using water or club soda and then soak it in warm water that has ammonia added to it, plus a liquid detergent. If the stain persists, you should try rubbing the stain area using alcohol and then brush it using soft strokes. For more instructions on stain removal, visit http://home.howstuffworks.com/how-to-remove-urine-stains2.htm.
Spray with (liquid) Oxy Clean. Then machine wash as normal. Now the most common mistake made when spraying a stain with stain remover is only spraying one side, as in the inside or outside of the fabric. Gotta spray both sides. Hope this helps! =)