There are electrically actuated solenoid valves on the pump manifold. There will be one exclusively for the offending slide. This valve is leaking by, based on your description. Some have a screw on the back side, you can ensure it is screwed all the way in (Do NOT overtighten! Snug only). These screw adjustments are used to bypass the solenoid valve (to manually operate, troubleshoot, etc). Power Gear is Lippert. Go to LCI1.com, support documentation, and you will most likely find your system and a .pdf service manual. Hope this helps . . .