Bath/Shower drains are designed to handle “brownwater,” i.e., potentially and occasionally lightly contaminated by fecal matter and urine…but not “on purpose.” OK, I’m not gonna get into the old discussion of peeing in the shower… I’d guess that quite a few people have done that without any harm. But pooping in the shower is going beyond the pale, so to speak. A (very)little bit of solid waste’s probably ok, but the proper place for fecal (blackwater) waste is in the toilet. The main problem with the bath/shower is its small diameter p-trap, which operates under low pressure. Solid waste will tend to accumlate there, leading to an offensive stink and potential heath hazard.
I’m new to this site, and I presume all the discussions are more or less serious…