Illinois Plumbing Code Practice

What should be the minimum size of indirect waste pipe compared to the fixture outlets?

1. 1/2 inch

2. 3/4 inch

3. 1 inch

4. 1 1/4 inch

The correct answer is: 3/4 inch

The minimum size of an indirect waste pipe is determined by the fixture outlet size to ensure proper drainage and prevent the possibility of blockage. According to plumbing codes, an indirect waste pipe should generally be sized larger than the outlet from the fixture it is serving. A common practice is to have the indirect waste pipe sized at a minimum of 3/4 inch for many residential fixtures, which allows for adequate flow and prevents potential backflow issues. This size is effective in managing the waste flow without risking back pressure that can occur if the pipe is too small. A 1/2 inch size would likely be insufficient for many fixture outlets, leading to drainage issues. Sizes such as 1 inch or 1 1/4 inch may be larger than necessary for certain fixtures and can result in increased material costs and complexity in installation. Understanding the appropriate sizing is essential for maintaining effective plumbing systems and adhering to local plumbing codes, which often follow guidelines set forth by models such as the Uniform Plumbing Code. This highlights the importance of ensuring that the waste pipe is adequately sized to handle the discharge from the fixture it is connected to.