The cable pull valves are an inherently poor application. It's like keeping a Ford 6.0 on the road. I know a guy who does but at great cost and effort. There is more than enough to maintain on an rv without having to adhere to an unnecessary maintenance schedule for waste tanks. Just my $.02.
Hi, I don't know much on camper cables but, I owned enough motorcycles to tell you that they make cable lubricators, that you can pump grease into cables. they clamp right on to cable and you use a grease gun to fill cable with grease. I didn't ride much in cold temps. but, I used high temp. wheel bearing grease in all mine, worked good for me. Just a thought, my 3000rk has rods and I used 3/8 fuel line and cut it down one side of hose and slid it down rods and I pour small amounts of cooking oil in the top of the hose and work it back and forth to lube valve. I also have the clean out option on black water tank that I run constantly, while dumping tank, then leave it running after I close valve, then I have wife flush toilet while I open valve to do final dump. This has worked good for us so far. Good luck to you and Happy Camping..