Simple garden hose quick release coupler. The O-Ring can also be found in my other models.

If your print leaks there might be several reasons: 

    (1) Filament dryness and printing environment. Wet filament and temperature changes lead to shrinkages or enlargements in the final print up so several mm. This is a significant delta which causes the O-Ring not to fit tightly. Solution: dry filament and control printing environment.     

    (2) O-Rings do not fit to printed model. This effect comes from very slight variations in O-Ring manufacturing tolerances and print-tolerances. Original Gardena O-Rings might be 0.5mm smaller than what the model would require to seal the space between adapter, O-Ring and quick-release on the hose itself. Solution: scale up the O-Ring from my models or use the slightly bigger version (coming up). My first advise would be to use a 5% scaled up O-ring printed from TPU.
 

How to test your print for the right dimensions:

Measure your print. The disc beneath the O-Ring slot should be 15.30 mm in diameter. 15.50 mm does still fit, 14.80 mm is to small and you need to adjust your filament or use a bigger O-Ring. 

This Adapter was modeled to be compatible with garden hose systems commonly found in german supermarkets and hardware stores. There might be other variations in the rest of the world that do not fit properly.