An in soil sprinkler i designed and tried. Found that the pump i was using didnt supply enough power to allow water to actually shoot from the holes but id like to think for the right pump this would work perfect.

The top of the sprinkler is designed to go into a 8mm pipe.

This was designed during part of a project i was working on for a self watering plant using a raspberry pi. My other sprinkler design is also uploaded if this one doesnt work for you.

Good luck and let me know how you get on