Downspout adapter

In a typical household radon remediation installation where the fan is located outside, it's customary to use regular downspout as the exhaust vent. In the installations I've seen, the installers "adapt" the radon fan's 3" pipe fitting to the downspout using a ridiculous amount of silicone caulk and nothing else.

I decided to make something a little more appropriate. This design accepts an Amerimax vinyl downspout elbow's smaller end, and in turn fits inside a so-called 3" PVC pipe fitting (w