This is the disconnected 'Impossible' stem. Fairly strong, works fine.

Add a picture from the four connector version
plus... my 'down to the last drop' filament spool to print it

Monoprice

Mini Delta

No

Yes

0.1

10% Cubic Subdivision

I used CURA 3.2.1 (Ultimaker version) as my slicer.

I printed mine at 205c on a 60c bed. I used a 5mm brim, and ZigZag supports set to 'touching build', set to 60% overhang limit. Four walls (shells), 10% infill with Cubic Subdivision (four walls and 10% infill is plenty strong - nothing more for infill is required)

Print speed: 150mm/s

Does it work? Yes. (I have used it with the pipe in the photo. -- For several weeks now - since I first posted this)
Will it be cleanable? Maybe. But not with a pipe cleaner.

Is it strong? Yes, at least the three connector version is. The four connector version should have better draw, but mine is still printing. I'll upload a picture of it when it completes. (Long since complete - works just fine as well. Three connector version draw is just fine, not much difference with four - just slightly more dramatic visually)

Try the test object first to see if you can get working airflow and can figure out supports. Why blow all the extra filament on the bigger stem?

I tried both Tree and standard supports. In each case CURA parked one inside the lower stem. You will have to dig that out. Should not prove too hard. It does not touch the inner walls (at least in my slicing.), but you can always use a drill bit if needed. (It popped out easily for me each time. I did run a drill bit that is just slightly smaller, to smooth out the walls slightly.)

I have included the Fusion 360 export files so you can see how it is done. Tweak it to fit your pipes, and style.

End to end, printed, it is about 105mm. The tenon is 11.5mm long.

The four connector version has a fatter lip, and the tip is rotated 45% to align nicely.

I would love to see your build too!