First of all urine, when coming directly from the source, is STERILE.
What should be noted is that urine is highly conducive to bacteria growth. So storing urine in any type of container, then being used as an anal douche/enema, the potential for complications increases dramatically. Things such as yeast infection, UTI in the male and female, kidney infection in the male and female and even a prostate infection in a male. Urine if left to sit long enough turns into AMMONIA. Doesn't matter if stored in an open air or air tight container.
However there are a few things to be concerned about.
The darker the urine the more acidic it will be, likely causing discomfort. And if held internal for any significant period of time could cause burns.
When the male urinates directly into the woman's ass, bacteria (from the female's ass) can find it's way back into the urinary tract. He runs the same risk of UTIs, prostate and kidney infections that he would if he were not using a condom during anal intercourse.
Obviously you want the male to be healthy and STD free. So no urine enemas from strangers or people with an unknown history of STDs.
Most women that become comfortable with the thought of a guy peeing in her actually enjoyed it. But there are those few that reported urine caused intestinal cramping when other 'recipes' did not.