I want to replace the thermostat in my Lowline 4-108, which has the aft heat exchanger and header tank in the front, and need to drain the coolant. Based on previous threads, I assume the pictured valve below the starboard side fuel pump is the way to do it, but it is stuck tight and I don't want to break anything, due to the horrible access. The hose coming toward the camera is just a short stub, and there may be (I can't see it well) a nipple underneath the "valve." Can anyone suggest a reasonable way to proceed?