Arizona Plumbing Practice Exam

Which plumbing fixture typically requires the largest diameter drain pipe?

1. Kitchen sink

2. Toilet

3. Bathtub

4. Washing machine

The correct answer is: Toilet

The toilet typically requires the largest diameter drain pipe due to the need to efficiently carry not just the wastewater but also solid waste away from the fixture. This is critical for preventing clogs and ensuring proper drainage. Toilet drain lines are typically designed to handle a larger volume and mass of waste compared to other fixtures. The standard diameter for toilet drain pipes is generally 3 to 4 inches, which allows for a smooth and effective flow of waste. For context, kitchen sinks and bathtubs usually utilize smaller drain pipes, often around 1.5 to 2 inches in diameter, which are sufficient for their respective uses. Washing machines also use around 2 inches; while significant, it is still not as large as what is required for a toilet. Therefore, when considering the need for a larger diameter to accommodate the unique demands of waste disposal, the toilet is clearly the fixture that requires the largest drain pipe.