This fitting (also known as a "bungalow fitting" or a "cottage fitting") is a sanitary tee that allows two trap arms to be connected at the same level. A toilet is the main connection, with the option of a right or left-hand outlet to the 3" inlet with a choice of 1-1/2" or 2" in size. It is used to keep stack-vented fixtures high to the joist space and thus conserves the headroom in a basement. As the water closet must be the lowest fixture, the smaller side outlet (usually used to connect the bathtub trap arm) enters slightly above the larger connection.