Gutter oil is a term used in China and Taiwan to describe illicit cooking oil which has been recycled from waste oil collected from sources such as restaurant fryers, sewer drains, grease traps and slaughterhouse waste.
SEWER DRAINS?
This is not just found in China - https://en.wikipedia.org/wiki/Gutter_oil
Here is a video concerning this travesty.
HOW do we know that any cooking oil transported to the united States from Southeast Asia does not contain this "gutter oil"?