CSLB Class B General Contractor's License Practice Exam

What is the minimum drain pipe size for the toilet in a residential home?

1. 2 inches

2. 3 inches

3. 4 inches

4. 5 inches

The correct answer is: 3 inches

The minimum drain pipe size for a toilet in a residential home is typically 3 inches. This standard is based on plumbing codes, which specify that toilets require a specific diameter to effectively handle the waste they generate and to ensure proper drainage. A 3-inch pipe provides the necessary capacity to prevent blockages and maintain efficient flow. Using a larger diameter pipe, like 4 inches, is often acceptable and can provide even better drainage, but the minimum requirement is established at 3 inches to ensure that plumbing systems can function properly in the vast majority of residential scenarios. Smaller sizes, such as 2 inches, do not provide sufficient flow capacity for a toilet, which is why they are not compliant with plumbing codes. Overall, understanding the requirements for plumbing fixtures, such as toilet drain sizes, is crucial for maintaining proper sanitation and operational efficiency in any residential construction or renovation project.