MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
Depends, if the thickness of the pipe wall is the same, you will get a little play, which is okay.
Be sure to scale up (80/70) in all directions, since the horizontal drain is preferably also round.
Other option, just make a round converter (in openscad?).