[riphay]

Don't mix up "Romans" and "Europeans." A better question is if the residents of Rome and other cities that had public facilities went back to the bucket or if they continued to use and maintain the public toilets. The rest of Europe likely never had public facilities to begin with, and the fall of the Empire might have delayed that technology transfer I suspect.

[dimitar]

There was a collapse of urban civilization. Rome's population went from around a million to about 50 000 people. Sanitation gets more important the higher the population density is.

[Symbiote]

The Romans took their technology to the end of their empire. You can see Roman toilets and plumbing in Britain.

[ziikutv]

Recall that a lot of Roman Engineering was based off of what they learned as they colonizes/conquered. Meaning these sort of civilized solutions likely existed in other parts of Europe.

I think they went back to using lower-level solutions because of the collapse as dimitar mentioned.