Massachusetts Plumbers Journeyman Practice Exam

What minimum water seal must floor/trough drains provide?

1. Two inches

2. Three inches

3. Four inches

4. Five inches

The correct answer is: Three inches

The correct minimum water seal that floor or trough drains must provide is two inches. A water seal is essential in plumbing systems to prevent sewer gases from entering the building through the drain openings. The seal acts as a barrier, relying on the height of the water to keep these gases contained. In most code requirements, such as those established by plumbing codes in Massachusetts and other jurisdictions, a minimum water seal of two inches is mandated for floor drains. This is the standard measure that ensures sufficient depth to maintain an effective barrier while still allowing liquid waste to pass through the drain. A seal of three inches or more, while more effective, is not typically the required minimum and would be considered above the necessary standard, which is why the answer provided does not align with the commonly accepted plumbing code. Similarly, four or five-inch water seals are unnecessary for typical applications and would add complexity and potential issues within the plumbing system without providing significant benefits.