For years I never understood how so much slug debris found its way into my drip irrigation systems. Then one day I broke off a plastic cap on one of the valves, only to see that beneath it was a favorite location for small slugs, etc. When the valves turn on, I could see how this debris enters the system. I understand the need for such a function, and understand why manufacturers hide this problem with a cap with a not-so-obvious big gap underneath it. I have broken off all the caps, making it easy to see and hose out the debris before I turn on the sprinklers in the Spring. Any other ideas on how to protect this area?
If you installed a filter on the line then the bugs wouldn't make it to the emitters.