What type of pipe fitting allows for four openings to connect a line at right angles?

The correct answer is a cross. A cross fitting is specifically designed to allow for the connection of four different pipe sections at right angles, forming a point where the pipes intersect. This type of fitting is commonly used in plumbing and sewage systems to create branching lines in multiple directions, facilitating the movement of wastewater or other fluids efficiently through a network of pipes.

In contrast, an elbow fitting is used to change the direction of the pipe, typically at a 90-degree or 45-degree angle, but does not provide multiple openings for connection. A coupling connects two sections of pipe in a straight line but does not offer branching capabilities. A union fitting allows for two pipes to be joined together and disassembled easily, serving a different purpose than that of a cross fitting. Understanding the specific functions of these different fittings is crucial for designing and maintaining effective piping systems in sewage treatment and related applications.