A 4-inch by 3-inch water closet connection must not be considered as what in size?

In plumbing, especially concerning drainage systems, the size of the connections is critical for maintaining proper flow and preventing clogs. When discussing a 4-inch by 3-inch water closet connection, it is important to recognize that the connection transitions from a larger pipe size (4 inches) to a smaller pipe size (3 inches).

A reduction refers to a decrease in pipe size from one section to another, which can create potential flow restrictions and increase the risk of blockages. In this context, the 4-inch to 3-inch transition is indeed a reduction because the diameter of the pipe is decreasing. Therefore, it must not be considered to be any kind of increase in size; rather, it reflects a smaller opening.

This understanding is essential when designing and implementing plumbing systems to ensure compliance with codes like the International Residential Code (IRC). Proper considerations about connections help in maintaining the efficiency of the drainage system.