It's a convention in fiction that characters are never shown using the toilet unless it's relevant to the plot, since nobody really wants to read about/watch/etc. characters going to the bathroom: not only is it boring but it's also fairly disgusting.
I want to have characters who aren't shown using the toilet because they don't need to. None of their species needs to, so toilet facilities are totally absent from their society. These characters are human apart from this change, and I don't want to have to add anything to the story that they do instead of going to the toilet, ideally. I do, however, want toilets not existing and characters not needing to use the restroom to be scientifically justifiable.
How can I make a humanoid race not need to use the toilet without making them different from humans in other ways that would significantly affect their lives?