Big Country sewer system schematic

We do not have drain a schematic. We had a similar problem with our 2014 Big Country 3070RE. Seemed to be at the point where the drain lines come together after exiting the tanks. Kept working at it with fresh water hooked to the flush tank valve and poking a small branch up the drain line a couple of feet. Finally got it cleared. We now carry a regular 15 foot drain rooter cable in case it happens again. We minimize the paper we use by using the community toilets where we stay. Also once or twice a day we fill the toilet to the rim using the half engagement feature of the flush pedal to send a surge of water through the black tank to purge it. To "mud maker" the lines merge after leaving the tanks... the tanks are separate.