Waste oil, the garbage flowing quietly in urban sewers. Some Taoists process it and turn it into "cooking oil" on the dining table. Every day, they fished out a large number of dim, turbid and slightly red pastes from there. After only one night of filtration, heating, precipitation and separation, these stinking garbage could be turned into clear "edible oil" and finally returned to people's tables through low-price sales. The main component of this three-no-products, which is called "gutter oil", is still triglyceride. In the traditional sense, gutter oil has seriously exceeded the standard in the total number of bacteria, biogenic amines, acid value, cholesterol, carbonyl value, malondialdehyde, heavy metals, acrolein and other indicators. Intake by human body will cause cell failure, induce many diseases and even cause cancer.