80mm Fan to DN75 HT-Pipe Adapter

I'am currently building a forced air solar thermal collector and here in Germany you can get HT-pipe (waste water pipe) really cheap so I thought, time for some unintended use as an air duct.

I will be using an old 80mm fan I scavenged from an old PC-PSU to create the needed flow of about 50m³/h. Since I did not want to use hot glue or duct tape (although this would have been the use case duct tape was designed for) to connect the fan to the duct work, I decided to make the fan part of a pipe