This is my attempt on providing a coupling for the Gardena system. I needed this for another project.
There is a .dxf with the profile attached, so just rotate it in e.g. Fusion 360. However, if you may need it, there is a .pdf with the sizes as well.

If you're just looking for a coupling to print, I got you covered, too. It comes with a 3/4" thread (untested though).

You need an O-Ring (10.5mm x 3mm) and a seal (24mm x 16mm x 3mm).

Artillery Sidewinder X1

No

Yes

0.2

20%

For outdoor use, PETG should be the best choice.

Use supports everywhere.