Master Plumber Practice Exam

What is the minimum size waste pipe required for a residential kitchen sink?

1. 3 inches

2. 2-1/2 inches

3. 2 inches

4. 1-1/2 inches

The correct answer is: 2 inches

The minimum size waste pipe required for a residential kitchen sink is typically 1-1/2 inches in diameter. This size is specified in plumbing codes because it effectively accommodates the flow of water and waste generated by kitchen use, including food scraps and other materials. A 1-1/2 inch pipe provides sufficient capacity to handle the drainage needs without risking clogs or backups, which are common issues in plumbing systems with inadequate pipe sizing. When considering the other options, larger diameters like 2 inches or 3 inches are not standard for kitchen sinks. These sizes are more suitable for main drainage lines or larger fixtures that produce greater volumes of waste. Using oversized pipes can lead to problems such as increased difficulty in maintaining proper drainage velocities and potential issues with venting. Therefore, while a larger diameter may seem beneficial, it does not align with the standard requirements typically established in plumbing codes for kitchen sink waste pipes.