A domestic dishwasher, with independent drain, has a drainage fixture unit value of _____.

The value assigned to a domestic dishwasher, which has an independent drain, is 2 fixture units. This classification is based on the Uniform Plumbing Code's guidelines that assess the load on a drainage system. In plumbing, fixture units serve as a standardized measurement to estimate the probable demand for drainage caused by various fixtures in a system.

Domestic dishwashers are counted as having a higher drainage requirement than simpler fixtures, such as sinks. The 2 fixture units reflect the anticipated volume of wastewater that a dishwasher might produce during its operation, taking into account the peak usage that occurs when multiple cycles run concurrently in a household.

In contrast, some other options represent either insufficient or excessive drainage values for dishwashers. For example, 1 fixture unit may be too low to account for the heavy usage during washing cycles, while 3 and 4 fixture units would overestimate the drainage requirements, leading to an unnecessary increase in pipe size or drainage capacity which can complicate the plumbing design and efficiency.