Clog/Black Pyramid help

We have tried a snake, we have tried filling the tank, we've stuck a hose down it with a sprayer. Those haven't worked. The pipe in this RV goes down, curves, then dumps into the tank. So, by reading more I'm thinking that this is a black pyramid issue. Maybe it's right next to the pipe that drops into the tank. So, how do you guys fix black tank pyramid issues. We left the tank filled for 4 days before trying to re-empty it, it just filled right back up again. I emptied the tank a while ago, a little came out, but not as much as I expected to considering the sensor in here read full. I don't know where that censor is located, but it doesn't seem that the tank is full rather than a clog near or in the pipe. Any suggestions?

Edited to say: There's a clog somewhere for sure because the toilet water is backing up into the tank. We can push the foot lever down and see water and tp in it.