Red Seal Plumbing Practice Exam

What is the minimum size of every building drain/sewer downstream of the main cleanout?

1. 3" (75mm)

2. 4" (100mm)

3. 5" (125mm)

4. 6" (150mm)

The correct answer is: 4" (100mm)

Every building drain/sewer requires a minimum size of 4" (100mm) downstream of the main cleanout. This is because this size allows for the proper flow of waste and helps prevent clogging. Options A, C, and D are all incorrect as they do not meet the minimum size requirement. Option A (3" or 75mm) is too small, which can lead to frequent clogging and backups. Option C and D are both larger than the minimum requirement and can cause unnecessary costs for installation and maintenance.