When my trailer was new the black valve leaked a little. When we got home I was able to (after emptying the tank) stick an angled spray nozzle up into the dump opening and spray around the corner at the black valve with the valve handle fully open. That cleared up whatever debris was clogging the blade valve seal and it's been fine ever since. I would try that first, and perhaps some spray lubricant on the handle rods and see if that helped. Last year I had to replace the black valve due to road hazard damage, and given how much fun that was if I was going to pull both valves to clean/refurbish the seals I'd probably just replace the valves, they are not expensive. I bought a Bristol valve since that is what Escape used, although I don't think there's really much difference between any of the major brands.