Yeah, honestly. I'm researching for a fic I'm writing, and many folks already had toilet paper even before 500 AD. The fall of Rome really messed up European bathing and toiletry habits since they apparently lost access and historical reference to plumbing systems, or didn't bother to install them when considering urban infrastructure (hence the occasional dumping of waste in the streets by 2nd and up-floor residents, even as late as the Victorian era, despite more modern plumbing existing by that point). Moreover, cultures that didn't use toilet paper already had pre-modern shower toilets and such. Not to mention the entire issue of air flow and cooling systems! They designed properties to accommodate air circulation naturally to keep the space to comfortable temperatures, especially in desert or hot climates (which makes the adoption of Western building methods as Top Tier a little disheartening, especially when they don't work for the area and require substantial HVAC system installations to be anything other than a hot oven).
...Ah, but enough of that. Medieval folks were a lot more intuitive and scientific than we think. It was just, well...wars, the Crusades, knowledge loss, poor information spread, the works. That's why I still mourn the loss of the Library of Alexandria, or any library, really. Who knows how much more advanced we would be if we spent less time burning books and knowledge just because of some sociopolitical scheme?
I think it's pretty cool how advanced people really were in medieval times. Even, depending on the society and region, had buildings that created ice by using geometry to cool the low area of the structure enough to reach freezing. Which is mind-boggling.
It also brings to mind just how much was lost from the fall of Rome and the burning of the Library of Alexandria. Did you know they'd actually created copies of the entire library and finished shortly before the library was destroyed? They were getting ready to send the copies to a new library specifically out of concern of something happening to the original.
Anyway, if medieval people were so advanced despite having lost almost everything (their knowledge, and pretty much all western knowledge originates from what was gleaned from a few surviving scholars and a handful of scrolls and tablets saved from Alexandria), then imagine just how advanced Rome and Egypt and other places around there truly might have been.
There's even a story from one of the ancient Greek historians about a time he went to Egypt and discovered what, from the description, is very obviously a lightbulb that activates from the bioelectricity radiating from peoples' bodies by proximity. That same guy recorded a conversation with a high ranking Egyptian priest about how one day in the far future, people wouldn't believe stories of their capabilities and they'd be relegated to myth and legend, just as they did to ancient societies before them (which is pretty telling on its own about cycles of civilizations).
So far as I know, the Crusades had no effect on technology or knowledge. They're also basically the opposite of what common knowledge says about them and what Hollywood portrays, same for the Inquisitions (yes, there were multiple, they even invented such things as humane treatment of prisoners, ending torture, and invented the modern foundation for investigation).
I think dumping waste in the streets was most likely just assholes being assholes. They
did have sewers in their cities. And of course, the public wouldn't tolerate literal crap being thrown on them all the time or the streets filled with it. The problem regarding the structure of smaller locations is that after the fall of the Roman Empire, there were a lot of warring factions, tribes, roving renegade armies, and so population centers tended to be built around fortifications and with small enough populations to shelter in those fortifications for extended periods of time. As a result, sewer systems weren't really needed as there simply weren't enough people or they could become a vulnerability. Same for water systems. But, the big, major cities still had sewers and, of course, those built before the fall remained (well, when not destroyed, obviously) and it was a pretty simple, basic construction project so probably was well-known how to make by a lot of people.
The biggest problem was the loss of medical knowledge. They were performing
brain surgery in in the ancient world. We went from that to leeches practically overnight.