Urine can't clean the vagina. Urine comes out of a different opening in the body (and ya wouldn't want the uric acid in the urine to clean such a sensitive area of the body anyway).

Are you a girl (because if you are, I recommend learning about the female anatomy). It's important for us girls to know these things.

And if we only have sex with a long-term partner/husband (and hopefully he's clean), we don't generally have to worry about cleaning the birth canal/vagina.