The plastic reducer is going to be modified with the magnets that @joe has listed to connect the PVC to the booster. The suction does an awesome job (until you turn off the fan).
Here are the Amazon Links:
For portable setup
Hydroplanet™ 6 Inch Hydroponic Inline Duct Fan 4inch 6inch 8inch Booster Fan (6inch)
https://www.amazon.com/gp/product/B019J979CO/
VIVOSUN 25 Feet 4 Inch Non-Insulated Flex Air Aluminum Ducting for Ventilation w/ Two 4 Inch Stainless Steel Clamps
https://www.amazon.com/gp/product/B01EUURUVM/
Hon&Guan Straight Duct Reducer and Increaser Adaptor Connector Inline Heating Cooling Ventilation Duct Fan 6" to 4" (150mm to 100mm)
https://www.amazon.com/gp/product/B06XCZRPJ7/
For the in house ducting
Hon&Guan 6 Inch Inline Duct Fan Exhaust Fan Mixed Flow Inline Fan Hydroponic Air Blower for Home Ventilation Bathroom Vent and Grow Room Ventilation Powerful & Silent Inline Fan 312 CFM (P series)
https://www.amazon.com/gp/product/B01MSWSTVQ/
Hon&Guan Variable Dial Router Centrifugal Inline Duct Exhaust Fan Speed Controller
Ideal-Air Stainless Steel Hose Clamps, 4 Inch, 2-Pack
https://www.amazon.com/gp/product/B00CJIFPBA/
Aluminum Tape / Aluminum Foil Tape - 1.9 inch x 150 feet (3.4 mil) - Good for HVAC, Ducts, Insulation and More
https://www.amazon.com/gp/product/B01FROBUXE/