Last summer the sprinklers worked fine but when trying to replace them with drip we found the water no longer flowed. I opened the pressure regulator to inspect if it was blocked but it seemed fine. I can hear the gurgling of water when I turn on the system either with the actuator or manually. But water just barely flows out and only at the first sprinkler outlet. There may be some dirt or stones in the pipes. Is there any way to clear out the pipes without water pressure? Or how can I troubleshoot the lack of pressure?