Hey everybody. I needed NPT threads on a part I'm about to 3D print. I came here expecting a solution but none were presented yet, so I thought I'd let you know how I made it happen.
All I did was go to McMaster and download a CAD file of a part with the threads I needed (in this case I downloaded a 3/8 x 1/4 NPT straight reducer). Then I just started removing features from the reducer until it was left with a threaded blank:

I made a hole in my main component where I needed these threads, alligned the threads with the hole, and combined the two geometries. Now I have the NPT threads I need and I can get to 3D printing.

It's a little unorthodox, but it absolutely works. Who wants to sit through a tutorial on manually cutting tapered NPT threads?
Good Luck,
Zach Martin