Outdoor poos?

I has confusion.

I sometimes poo in my poo tray, which is full of stones, but I prefer to poo outside.

But... I've only ever seen my human poo in the big white thing that he sits on.
I'm not sure where the poo goes. There must be little stones at the bottom of the big white thing, like the ones in my tray.

I've never seen my human poo outside though. Surely he can't just poo on the white thing - that would be odd.

Maybe he only poos outside when I'm not around. 

Strange.