This is a good idea. But a quick search shows 3” PVC cap has an inner diameter of ~3.25”.
The mechanical tubing I used has an outer diameter of 3.5”.
I’m pretty sure the schedule 40 pipe also has an outer diameter of 3.5”
Looks like a 3.5” PVC cap would work, but they are a bit more rare. Doesn’t seem like the hardware stores really have them. Might have to order on Amazon.
And actually, I remembered my buddy has a 3D printer he doesn’t really use. Maybe he would be happy to break it out for this project