Charlotte Pipe 6 in. PVC DWV 90-Degree Hub x Hub Elbow Fitting-PVC 00300 1600 - The Home Depot
Vent Systems 8" inch to 6" inch Duct Reducer Adapter Connector Fitting Pipe Increaser Reducer Cone for HVAC Ventilation Systems, ABS Plastic PVC Pipe 200 to 150 mm - - Amazon.com
Charlotte Pipe 6-in x 6-in Dia Schedule 40 Coupling in the PVC DWV Pipe & Fittings department at Lowes.com