Since vampires no longer digest food it would seem that evacuating their bowels would be a practical event during their conversion. I agree this lore should be reflected upon more.
It's actually the incentive for new vampires to be made. During the turning process food is curtled and turned into a special type of feces Wine liquor. Patron vampires then spend the turning process Licking the rich secretions from the vassal vampires anus.
Really the whole thing is an intimate and beautiful process.
I have never wanted to un-read something so bad in my entire life. That's in my head now, and it's all your fault, and I curse you forever because of it.