The one-piece spun aluminum body has a TPO coated flange for direct hot air welding of TPO roof membranes. The drain flange has a depressed sump area for improved flow and to facilitate drainage. The TPO RetroDrain is equipped with a heavy duty cast aluminum strainer dome for strength and durability, and incorporates U-Flow® Seal technology, providing a mechanical watertight connection to PVC or cast iron pipes.