Yesterday two of the grandkids came by while their Mother was at work. The least one, Zachary, immediately noticed the slab in the back yard. Zach is four years old.
See arrow below. You can click on the picture for a larger version.
That red arrow points to the drain for the toilet. Zachary walked on to the slab and I was showing him the drain pipes and how they work when my attention was diverted by Milady walking out the back door. I watched her for a moment then turned back to see Zachary with his pants down around his ankles, peeing down the drain.
I turned back to Milady, who was grinning widely. I shrugged. That's what it's for, I guess. He won't be the last one to pee down that pipe, but I'm hoping to finish it before we open it for business.