When Spike complains that Twilight gets to use the bathroom, she complains that he has more places to poop than her. So, Spike dares Twilight to pee and poop anywhere other than the toilet for a whole day. Twilight is also very gassy. (EqG Twilight and Doggy Spike, of course)
Then, Sunset Shimmer joins in on the fun.
Contains: Scat, fart, watersports. Not recommended for those who neither have the fetishes nor find them funny. Might also not be too terribly detailed but I am trying to write better. Don't take too seriously.
Done by request.
I tried to put more detail in it, but I fear it's, once again, just fetish fuel with no real story to them, and will be very disgusting to anyone who neither has the fetishes nor finds them funny.