Even with regular use of expensive drain-valve lubricants that are poured in tanks, I’ve struggled for years to operate sticky dump valves. Removing and lubricating at least the black-water valve once a year, and sometimes even replacing valves, was just a temporary fix. Then I came up with a simple and very effective solution: 1) With the valve closed, drill a small hole on the handle end of the valve. 2) Insert the strawlike nozzle that is typically supplied with spray lubricants into the hole and fill the cavity behind the valve slide gate with the lubricant. 3) Operate the valve several times to be sure to distribute the lubricant, which will make the valve easy to open and close. 4) Seal the hole with a small screw. 5) After a number of uses, when you notice that operating the valve takes more effort again, relubricate. I use white lithium grease or a silicone lubricant.
I wish I had come up with this idea 25 years ago! I can tell you from firsthand experience that it is not fun to lie down under the trailer at a dump station and remove a firmly stuck valve when your RV’s black tank is full.
Ralph Clark, Albuquerque | New Mexico