What may not be used in the vertical position in a plumbing system?

The double sanitary tee is specifically designed for use in horizontal applications, where it allows for the connection of multiple horizontal drainage lines. When positioned vertically, the design can cause blockages and improper drainage, as the configuration of the fitting does not facilitate the effective flow of waste materials. In a vertical orientation, the risk of creating traps or obstructing the flow increases, which can lead to drainage issues and the potential for venting problems within the system.

On the other hand, the other fittings mentioned can be appropriately employed in vertical positions. Sanitary tees are designed to accommodate branch lines connected at 90 degrees, suitable for vertical or horizontal installations. Cleanout fittings are essential access points for maintenance and can be installed in various orientations, including vertical, to provide proper access to drain systems for cleaning. Wye fittings, designed to connect three pipes at a 45-degree angle, can also be used in vertical configurations while supporting effective drainage flow without the complications presented by the double sanitary tee.

Understanding the functionality and appropriate application of these fittings is crucial for ensuring a properly functioning plumbing system and preventing potential issues related to drainage and venting.