blocked black & grey water tanks

Im in a 99 rexhall rexair, i went to drain the tanks like normal, apparantly i left the valves open last time, after i used the flush system for 5 minutes i opened the valve. i had mainly fluids come out than it clogged, tried to fill it up to push it out (which had worked previously) now im stuck with an almost full tank and a clog. A tiny amount of fluid seems to build up past the clog when you leave it alone for awhile. After research im fearing a pyramid. I even tried filling up the sewer line with water and lifting it above the tank to back flush it, but it didnt work. Also tried taking it for a short drive. My wife dumped a gallon of bleach down the drain yesterday. In a week ill be taking it for a 4-5 hour drive.

Best thing i got on my own is treat it with some ridx and drive it in a week and hope it dumps whe i get there. This however is not ideal obviousy.

Calling a professional is a last resort and i dont need advice on how to do that :)