Liz, I'm hurt.
What kind of person do you think I am?!? Of course I wouldn't leave him there; if I have to, I absolutely would.!
She knows I'm a bit squeamish, and she knows she's better at it anyway; so the timing works out that she's got him changed and ready for bed before she goes out. And she's usually not out for long.
Anyway, bottom line, if the kid poops and I'm the only one there, it may take a while and some smelling salts, but I'll do it; and I'll even do it well, dammit!