With a tape measure, determine the desired height of each sprinkler head. The top of a pop-up sprinkler should be level with the soil surface, and the riser for a stationary sprinkler should be high enough that foliage won’t block the spray.
If you use a cutoff threaded riser, cut it to the desired height and recheck the height after it is cut. Wrap the riser threads with pipe-thread tape and screw it into the tee fitting.
Open the shutoff valve that supplies the irrigation system. Next, briefly open the control valves by hand to purge any dirt, PVC shards, or dried glue, which often clog new sprinkler systems.
With the trenches still open, work quickly. Avoid letting the water run for as long as you would to flush an established system, and don’t flood the trenches.
Screw rotors and spray-head bodies to the risers, making sure not to get any dirt into the pipes. Most spray-head bodies come with flushing caps that have a hole big enough to allow any debris still in the system to escape. Flush the system again and then replace the flushing caps with the appropriate nozzles.