Try an easy cleaning! Use a garden hose and the adaptor that came with your unit, snapping the end right onto the top coupler. Turn the water on, gently at first, and start priming the injector with water (check valves can handle reasonable water pressure so don’t worry). Pump the handles 10-20 times. Turn off the water and remove the hose end adaptor. There should be some water in the top coupler. Pull back the handles and if the injector is primed, water should be drawn into the injector. And now you are ready to care for trees properly.