GenExhaust Universal Exhaust System Double Layer Wall Attachment for 1-1/2" ID Steel tubing

Is there an exhaust that will fit a duel fuel Westinghouse 1250 generator?

How do you install through an osb wall (shed)? one of your pictures suggests just routing directly through wall. should i use a thimble of some kind?

I have a champion dual fuel 9000 whatts and i want to make it as quiet as possible. How many decibels with this muffler?