Changing fixed dump valve to flexible cable controlled valve

dryfly wrote:
Could you just re-plumb and get the valve out closer to the side of your trailer? Or, mush easier, use one of the valves that connects to the bayonet fitting on the drain pipe and leave the original valve permanently open.

This is the easiest, cheapest, and best solution to this problem.
I also have the galley drain under the slide, what a stupid design. I think I paid ~$35 for the thing. It has it's own valve, so no other surprises either.