Long ago, I worked at an Asian restaurant in the US, and my friend came to visit me from out of town. He drove a diesel Volkswagen Rabbit that he had converted to run ​on vegetable oil, so he had me ask the restaurant owners if he could have some of their waste oil from the fryers, and they said "Sure." Now, he obviously couldn't use the oil with all the fried up bits of wonton and eggroll wrapper, so he had to filter all that gunk out.

👆That's what it looked like.