Plumbing

I had the plumbers at my house yesterday and it occurred to me to wonder: Isn’t plumbing really an instance of the “extended gut”? Isn’t it rather arbitrary where we conventionally think the digestive system leaves off? What if your colon were replaced with a PVC prosthesis and extended further out into the environment? What if a creature were born with a whole plumbing system attached to it? We refer to our digestive system as our plumbing; can’t we also refer to our plumbing as our (extended) digestive system? It’s all just a way to dispose of waste products produced by eating.