Risers with a diameter of 4 inches require what size drain pipe?

For a riser with a diameter of 4 inches, the appropriate size for the drain pipe typically should be larger than the riser itself to ensure effective drainage and prevent backflow or drainage issues. The rule of thumb in plumbing and drainage design is that the drain pipe should have a diameter that is either the same as or larger than the supply or riser pipe it connects to.

Choosing a 2-inch drain pipe does not align with best practices in drainage design. A 2-inch drain may not adequately handle the volume of water flowing from a 4-inch riser, potentially leading to clogs or insufficient drainage. On the other hand, a 3-inch or 4-inch drain pipe would be more appropriate choices to ensure that the drainage system can handle the flow effectively and maintain adequate pressure throughout.

In general, when designing or evaluating plumbing systems, it’s crucial to select pipe sizes based on proper codes and standards, which usually stipulate that the drain size should meet or exceed the supply line size to facilitate efficient water flow and prevent any potential issues with backpressure or drainage capacity.