How to drain the water from the oil-water separator of the truck? There is a protruding knob under the oil-water separator. Just loosen it until the gasoline comes out: 1. If there is water and impurities in gasoline, the parts of fuel system will be corroded and rusted by the water in fuel. Removing water from diesel oil is very important for trouble-free operation of fuel system and prolonging its service life. 2. Oil-water separator is mainly a separator that removes impurities and moisture by gravity settlement principle according to the density difference between water and fuel oil, and has separation elements such as diffusion cone and filter screen inside; 3. The oil-water separator has other functions, such as preheating fuel to prevent wax deposition and filtering impurities. @20 19