After finding out WHY he is doing these things, I would probably start having him take showers. He can't bathe in pee. But, he can pee in the shower.
But, beyond that one idea, I would really look for a possible problem. There may be absolutley nothing. But, it's something to explore.
Have you talked to him about it? Sometimes the best time to talk is in the car when the two of you are alone. He's a captive audience, and kids are sometimes more willing to open up when you aren't looking directly at him.