Ah...that reminds me. Centek makes spun fiberglass unions for this type of stuff. When I removed my flapper that Neil mentioned (because the pin broke and the flapper was not flapping) I used a Centek elbow.
If I am sailing in following seas so rough I have to worry about back filling the exhaust, I didn't check the forecast close enough and should stay anchored or tied to the dock.
https://www.centekindustries.com/ - but you can buy it at Defender, Amazon, etc.