What is the maximum slope allowed for a drain line in a residential plumbing system?

The maximum slope allowed for a drain line in a residential plumbing system is 1/4 inch per foot. This slope is considered optimal because it allows for efficient drainage by ensuring that wastewater flows downhill without significant risk of stagnation or blockages. A slope too steep, like 1/2 inch per foot, can lead to rapid drainage that may cause solids to be carried away faster than liquids, potentially resulting in sediment buildup and clogs. Conversely, a slope that is too shallow, such as 1/8 inch per foot, might not provide sufficient gravitational force for effective drainage. Therefore, maintaining a slope of 1/4 inch per foot strikes a balance that helps facilitate consistent flow while minimizing maintenance issues in the plumbing system.