What is the minimum slope required for a 4-inch diameter drain pipe?

The minimum slope required for a 4-inch diameter drain pipe is 1/4 inch per foot to ensure proper drainage. This slope is critical because it helps facilitate the flow of wastewater by using gravity to move the effluent through the pipe. A slope that is too shallow can result in the accumulation of solids within the pipe, leading to blockages and inefficient drainage, while a slope that is too steep can cause turbulence and potential issues with proper water flow.

While other options suggest lesser slopes, they do not meet the code requirements necessary for effective drainage. A slope of 1/8 inch or less per foot could delay the movement of waste, causing potential backing up and sanitary issues. Therefore, adhering to the established minimum of 1/4 inch per foot for a 4-inch drain pipe is essential for maintaining a functional plumbing system.