Which fitting is used to connect a horizontal waste line to the vertical section of a waste stack?

The single sanitary tee fitting is specifically designed to connect a horizontal waste line to a vertical section of a waste stack. Its design allows for efficient flow of waste and is essential in maintaining proper drainage and ventilation in plumbing systems. The horizontal branch enters at a 90-degree angle to the vertical pipe, which helps to prevent clogs and ensures that waste can move smoothly downward without creating air pockets.

In situations where waste lines need to branch off from a vertical stack, the single sanitary tee facilitates this connection while helping to maintain the direction of flow. This is vital in plumbing installations to ensure compliance with codes and effective operation of the drainage system.

Other fittings such as a double wye fitting are typically used to connect multiple horizontal pipes in a more complex arrangement, and a coupling is meant for straight connections between two pipes of the same diameter. A P-trap serves a different function altogether, primarily for preventing sewer gases from entering buildings, rather than connecting different orientations of waste lines. Thus, the single sanitary tee is the appropriate choice for this application.