Thanks Chuck,
Whew, that was almost like doing my first colonoscopy, except none of the anatomy was familiar
It really looks like whoever owned your trailer before left the tank full with a leaky dump valve and over time, as the water drained out of the tank, "concrete" was all that remained. I sure don't envy you the job of breaking that stuff loose and getting the tank clean, but once you do, assuming you don't poke a hole in it while cleaning, I think you'll have a lot more usable black water storage capability.
That video is a perfect example of what not to do when storing your RV. What might seem like a "convenient" way to camp, the attitude of, "It's only half full, I'll just empty it next time we go camping." can be a trap that sets up this kind of problem. It's so much easier to take a couple of minutes to dump AND flush the tanks so you know this kind of buildup won't occur.
Oh, you might want to be extra careful with that black tank valve. I can't remember if you've changed it out or not, but I'm pretty sure it's got a slow leak and that is what caused the initial "dry tank" problem.
Thanks much for posting the video, it's definitely an "eye opener"
