Branch and building drains downstream of the third WC fixture drain connections shall not be less than?

Branch and building drains downstream of the third WC fixture drain connections shall not be less than?

• A. 3 inches
• B. 5 inches
• C. 6 inches
• D. 4 inches

Answer: (D)

Branch and building drains are sized to handle the combined flow from all fixtures that discharge into them. As you add more toilets, the total discharge increases, so the pipe must be large enough to carry that water without clogging or slow drainage. Beyond the third WC connection, the minimum diameter must be increased to 4 inches to provide sufficient capacity for the cumulative discharge while maintaining proper drainage performance. A smaller size would risk backups and poor flow, while larger sizes (like 5 or 6 inches) are not required by this rule.

Branch and building drains are sized to handle the combined flow from all fixtures that discharge into them. As you add more toilets, the total discharge increases, so the pipe must be large enough to carry that water without clogging or slow drainage. Beyond the third WC connection, the minimum diameter must be increased to 4 inches to provide sufficient capacity for the cumulative discharge while maintaining proper drainage performance. A smaller size would risk backups and poor flow, while larger sizes (like 5 or 6 inches) are not required by this rule.