Changing fixed dump valve to flexible cable controlled valve

I have used solid and flex dump valves. I have installed both types myself. I much prefer the solid valve rod because it works better. If it were me I would look into lengthening the rod on the valve you have now. Unscrew the T handle, screw on a long nut and rescrew an extension rod with support. Doing this will be easier than replacing the entire valve.

http://rvsupplies.com/valterra-waste-valve-extension-rod-kit-10-to-12-carded/?gclid=CP_KlN2Y6NMCFYhMDQodSVAMpQ