Last summer 2000 miles from home, my black valve did the same as yours. I hammered it back in with a rubber mallet. Took it to a RV repair place. They said I needed new valves but would take 2 weeks to get the ones required for my tank.We would be on our way home by then. I had an end of line twist on valve already on. The repair place said they could open the valve and I could just use the end of line valve, which I did. I took the 5er into my dealer when I got home and they replaced the black water valve cable and one gray water valve cable as it was going bad also. I just used them for the 1st time while out camping a week or so ago and they worked fine. So before replacing your valves I would see if it just the cable and can you get just the cable or do you have to but the valve assembly as well.