this happened to me in Yuma last year. I dumped the black tank and got to doing something else and forgot the valve was open, so I found out when the tank got full the next time around. What I did is I went to a rv dealer who told me I had maybe two choices, use a waste digester or have a guy come out to see if he could pump it out. buying the digester is a lot cheaper so I went with that option. I poured two bottles in , added water to the top and let it set for three or four days. we were lucky we had a bathroom in the little house we were next to. in that length of time the stool was fluid enough to drain when I opened the valve. then I clean out the tank with a flushing wand and counted my blessings. I will never dump again and leave the area until the tank is empty .
