The second law of thermodynamics dictates that everything poops.

Anything alive that is using energy and doing work and transforming matter must poop in some form or another.

We don’t know what form life out there might take, but we know it poops.

Even post biological machine life would poop in the form of industrial waste, waste heat, etc.

Even near perfect recycling can only be near perfect, not perfect, due to the second law, which means a super efficient organism or closed cycle ecosystem or industry will still poop. Just not much. It will also emit a ton of waste heat, which I guess is kind of poop since mass and energy are ultimately equivalent.

If there’s weird life out there made of plasma or something, it poops. Probably charged particles or something.

The monolith in 2001? It poops. Somehow.