water connector M75 to G1' for 1000l water tankThreads are modelised a little larger than ISO sizes to fit corectly whit market tank.Nylon can help tightness. It's possible to add a seal d=60mm for better tightness.Notches are designed to help screwing with a wrench.See in pic 4 parameters for 3D printing:The thinkness of layers is 0.2 because 0.3 is to much to have precise threads and 0.1 is to small to be strength.You need to set Horizontal holes expansion at 0.2mm otherwise it is not sure that it will work.Wall line are 50 to be sure that the part is full and ensure strength.Make sure there is no support on the threads to keep this clean.You can print it with PLA PETG or hard TPU to ensure tightness.

Printed, tested and approuved