a plumbing focus - This person is obsessed with what goes in and what comes out

This person is obsessed with what goes in and what comes out of the lowest part of the body and how it all works.

I can spend an hour watching videos about how toilets work and why people always get stuck in the bathroom.

My main goal in life is to figure out why my dad always says he's 'not done yet.'

I once asked my teacher if we could do a science project on farts and poops. She said no. I cried.