Master Plumber Practice Exam

What diameter does a standard sink trap typically have?

1. 1 inch

2. 1-1/4 inches

3. 1-1/2 inches

4. 2 inches

The correct answer is: 1-1/2 inches

A standard sink trap typically has a diameter of 1-1/2 inches, which is the common size used for kitchen and bathroom sinks. This diameter allows for adequate drainage capacity while minimizing the risk of clogs. The 1-1/4 inch size is also a valid option for smaller sinks, mainly in specific applications, but it is less common for standard use. Larger diameters, such as 2 inches, are typically reserved for areas with higher waste removal requirements, like floor drains, and are not suitable for typical sink applications. The 1-1/2 inch diameter provides a balance between effective drainage and manageable pipe size, making it the preferred choice for the plumbing code and standard practice in residential installations.