Girls pee out of their butts. (part three)

The first conversation on this subject, described in part one, came to me in the middle of earning my Women's Studies degree. Now, I'm a year out of school. I'm nannying for 1.5 year olds and writing on the side, and I came home for a week to see my family. I spent most of the day, today, with my 4 year old nephew. He's well-spoken and curious, but also a bit modest at times. Though today he came into the bathroom with me at the restaurant where we were eating lunch. When I sat down to go to the bathroom, he unabashedly searched for the source of my pee. I asked him if that's what he was looking for, and he smiled, "Yes. Do you pee out of your butt?"  I explained that just like he has a penis, I have a vagina, and that it would be funny if we peed out of our butts. And we laughed. (Though my mom did point out later that we actually pee from our urethra. But I knew that's not what he was getting at.)

He didn't say another word until we were in the car later and he decided to tell me, as a joke, that girls pee out of their penises. Now, were he my kid, it would have been a bigger opportunity to explicitly discuss the fact that some girls do in fact have penises and some boys have vaginas. Though I am his aunt. I can't go full feminist on the kid then leave him hanging when I head back home to NYC. I only see him a few times a year. But I can at least plant a few seeds so that when he's 14 and curious, he knows who to talk to.
I said,

"You know, some girls do have penises and some boys have vaginas."
"Why?"
"Just because they do. Everyone's different."
"Oh."

And he simply continued with the former conversation;

 "Well boys pee out of..what's that word again?"
"Vaginas"
"Boys pee out of vaginas!"
*snicker*

This continued for awhile, and I felt accomplished.  I taught him a useful word today, though it wasn't much of an anti-transphobia teaching moment.