During the installation of a new stormwater drainage system for a commercial building, the plumber is connecting a roof leader to an underground storm sewer. The roof leader is 100 mm PVC, and the storm sewer is 150 mm PVC. What type of fitting should be used to make this connection?

Question: During the installation of a new stormwater drainage system for a commercial building, the plumber is connecting a roof leader to an underground storm sewer. The roof leader is 100 mm PVC, and the storm sewer is 150 mm PVC. What type of fitting should be used to make this connection?

Answer options:

• A 100 mm to 150 mm reducing coupling.
• A 100 mm to 150 mm eccentric reducer. ✅ A 100 mm to 150 mm concentric reducer.
• A 150 mm to 100 mm increaser.

Correct answer: A 100 mm to 150 mm concentric reducer.

Explanation: A concentric reducer is used to connect pipes of different diameters when their centre lines need to remain aligned, which is typically the case for vertical or horizontal connections where drainage flow can be turbulent if stepped. An eccentric reducer is usually for maintaining a flat top or bottom, often in horizontal runs to avoid air pockets or allow full drainage.