Ahh. Manteca. When I was a kid I used to ride from Stockton to Manteca as well. There was one bike shop there that my friends and I would visit there.
Once we got caught in the rain on the way back home and our jeans were soaked. A couple of us had to pee and since our jeans were soaked anyway we just let it go. The urine ran down the soaked jeans like a rain gutter and warm our legs at the same time. A very interesting sensation indeed!