So looking at the Straight Dope I rediscovered Fatbergs, which deposits of fats, cooking oil, and grease, wipes, and other stuff that hardens up in sewers causing them to back up. Really expensive to remove...
https://www.straightdope.com/columns/re ... e-upon-us/
Bright side. is that they can be used foe Biofuel... I thought everyone had the sense to not to pour grease and used cooking oil down the drain...