Three inch horizontal drainage piping shall have a grade or slope of not less than ____ inch per foot.

The requirement for three-inch horizontal drainage piping to have a slope of not less than 1/4 inch per foot is essential for ensuring proper drainage. This specific slope allows for effective gravity drainage, which helps facilitate the movement of wastewater and prevents the accumulation of solids within the pipes.

A slope of 1/4 inch per foot strikes a balance that is steep enough to promote flow but not so steep that it could lead to increased wear and tear or potential disruption of flow due to excessive velocity. Maintaining this slope is crucial for the prevention of clogs and for ensuring that the system operates efficiently.

Other slope options, such as 1/8 or 1/2 inch per foot, do not meet the minimum guideline needed for this size of drainage piping. A slope of 1/8 inch per foot is too shallow to effectively carry away waste, while a 1/2 inch per foot slope might be unnecessarily steep for a three-inch pipe, which could result in issues like increased erosion and turbulent flow that could disrupt the intended drainage function. Thus, the specification of a minimum slope of 1/4 inch per foot is vital for the proper performance of horizontal drainage systems.