A spraying system to be used on wastewater settling tanks for skimming the top scum layer into a drain. The system includes a spray nozzle that causes the top liquid layer to move in a circular fashion about the center of the tank. The nozzle can be in the form of a wall mounted spray unit that sprays water onto the surface of the contained wastewater. The nozzle can also be in the form of a multiorificed tubular body mounted directly onto the top of the drain trough. Water sprayed from the latter nozzle is directed into the trough and thereby causes a suctioning of the scum layer into the drain. The system can employ either of the nozzles or both nozzles in combination.