The way the Pink Eye virus can spread through poop is through hand to eye contact.
If you touch your own poop or someone else's poop and you or they have the pink eye virus in their body then if you don't thoroughly wash your hands after making hand contact with the poop and then touch your eye then that's how Pink Eye can spread through poop.
Always wash your hands thoroughly after wiping your butt or wiping your child's butt as well.