A separator provides improvements for better separation of an effluent into constituent parts and greater ease of use. A tapered basket provides improved flow and better filtration. A baffle directs effluent into the basket with greater force. An asymmetrical flange prevents mis-orientation the basket and baffle. An improved oil valve provides a locking mechanism to prevent dislodging of the valve during cleaning. An alternative valve uses a sensor to sense an oil/water interface and close the oil valve appropriately. A top seal prevents leakage of effluent at connection points with the lid of the housing. An underground unit allows below floor level installation of the separator. A bidirectional unit can be reversed to provide flow in either direction. A dual purpose tank can be used to store both separated oil and oil from operations for common removal.