The Romans didn't invent the toilet.
Regardless of whether they invented it, they used running water to carry away their feces.
Just google "Dark Ages not used anymore" and you'll find plenty to read.
I have read plenty about the topic and have seen some public TV shows about it. In all of what I read and heard, I never saw anything about medieval society using running water.
I'm not going to derail the topic further. Suffice to say that apart from Romanist [very devoted fans] and people who don't know any better, the idea of western Europe descending into some blighted pit of ignorance and suffering because they didn't have the Romans around to enslave them run things for them is no longer accepted by credible historians.
I never said that any backwardness of medieval society was the result of the Romans not being there to run things, although I did imply (rather subtly, I admit) that medieval society was backwards because the Roman Catholic Church was there to stifle free thinking. But yeah, we should probably get back to the topic instead of debating this further. On topic, I am no fan of the Imperial Empire because they put my head on a block during what I can only describe as a well done and emotionally charged opening scene.