Water that has been contaminated with light fluids is kept in the oil separator for a certain period. Due to the lower specific weight, oil droplets rise to the surface. Treated water drains from the oil separator through a run-off. When a limit amount of light fluids is accumulated in the trap, the fluids must be pumped through the entry shaft.
The gravitational oil catcher is to be dug into the soil. They can lie on drive-over surfaces or other. They must lie on an accessible spot for maintenance.