What is Used Cooking Oil?

Used Cooking Oil (UCO), also known as used vegetable oil, is oil generated continuously or discontinuously in all kinds of establishments that elaborate edible products, and which has suffered from any heating processes that altered its original characteristics.

...when you pour UCO in drains and sewers, it sticks to the walls of the rain drainage piping resulting in the reduction of its water evacuation capacity up to the point of blocking it and even causing flooding?