“Outside of Venice, which used the Adriatic to rotate the sewage in and out, Europe was pretty nasty from about 535 AD to probably the 1200s ~ when one of my ancestors figured out the best place to build his castle was ON TOP OF THE RIVER so he could have “flushing toilets” in every room.”
Might I point out that the UNITED STATES did not have plumming at it’s inception, and plumming and sewage were not generally implemented untill the late 1800’s in this country (remeber out houses?). Yet, the U S was ahead of most nations from the time of the Declaration of Independence. We were a nation of simple farmers, but we also had great minds like Franklin, Washington, and Jefferson. Your point that Europe was so backward because of the implementation of toilets is pretty weak. Parts of europe were indeed backwards, but there were islands of knowledge and greatnest that persisted though the middle ages. The backwardness of europe in the middle ages is a myth itself and should be put to bed. The mighty caliphate was defeated for hundreds of years in the east by the EUROPEAN Byzantine empire. Islam was indeed ahead of Europe for a while, but this is generally exaggerated.
There were few centers of learning and intellect anywhere in the world from about 535 (give or take a couple of years) and the 900s. Europe certainly didn't have many of them in that period. Most people were more concerned with avoiding wild boar, wild bear, wild wolves, disease, roving bands of thieves and marauders, and so forth.
Even Byzantium got shut down pretty much for 85 years, and when that period was past there were Slavic speaking people living in Greece itself (where'd they'd been prohibited since the days of Pericles, and that crowd).
Venice was still young the day the Dark Ages started, and it took them a couple more centuries to begin the recovery ~ and when that happened they were very much alone. The Renaissance occurs in the 14th to the 17th century, in the Late Middle Ages ~ however, I'm sure you have the Carlingian Renaissance in mind, and that occurred during the late eighth and ninth centuries.
Islamic Spain got a kick start in the EARLY eighth century and didn't give up its lead until the Christian takeover in the 15th century.
Now, regarding toilets, that's what those moats were about ~ early Middle Ages counts discovered that if they dumped just everything into the surround it would keep the enemy at bey ~ along with the wild animals ~ and, if need be, the equally dangerous peasantry.
Americans were much more fortunate. It was feasible to make use of outhouses because there was lots and lots and lots of land. You do have to shut the things down recurringly and relocate the box to another hole. That means you need a large backyard! Even today Europeans need to use sewers. Still, it's possible that in the Early Middle Ages after the population crash folks got along fine with outhouses and trenches. I'll see if someone has written a definitive book about that. There are books that cover the castles, of course, but you don't get the really fancy jobs until the 1200s.