Grady from Practical Engineering makes great videos to explain basic concepts of engineering, and some not so basic ones. This one shows you how sewers are designed, what makes them work, and what can block them. You always learn new things, like how to make a sewer go under a river, and a few good engineers' sayings; "sewers are lawless places by nature".
I really like the demonstration of how quickly toilet paper dissolves compared to wet wipes – don't flush them!
After watching this, it is very hard not to go down the rabbit hole of simulated sewage (or "fake poop"), so I will probably post about it soon...
More information: How Sewers Work, by Practical Engineering