I would never order a meal in such a place, because I could never be certain where their cooking oil came from.
Gutter oil or sewer oil is a general term for oil that has been recycled. It can be used to describe the practice of restaurants re-using cooking oil that has already been fried before. It can also be used to describe the processing of waste oil collected from sources such as restaurant fryers, grease traps, slaughterhouse waste, and fatbergs.
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