To make it easier on yourself there should be a way to put a float switch in the sump and automate the system. A float switch could be ran in parrallel with the wall mounted switch. Then any little bit left could be pumped manually. I plan on building a sump for mine to keep the bilge dry. It will be fairly simple and I plan on retro fitting a bilge
pump and seperate float switch to accomplish it. As for that switch in your companionway have you checked it for voltage across the terminals when in the off position to see if there is anything running through it or if its dead?