A method for pretreating a wastewater stream containing grease and food particles before the stream enters a sewer includes the steps of directing said wastewater stream to a separation area; directing said wastewater stream along a preferred flow path within said separation area, said preferred flow path being sized and shaped to permit said grease to rise out of said wastewater stream; trapping said grease which rises out of said wastewater stream; extending a wastewater outlet substantially across said separation area; accelerating said remaining wastewater, carrying said food particles, through said outlet from said separation area, thereby sucking said food particles away from said separation area; and directing said wastewater and said food particles toward said sewer system.