Last fall I was cleaning out my tanks at home. As a final conclusion, I rinsed out my sewer hose in the grass near where my camper is parked. When I flushed out the hose, everything appeared to be OK, no problem, nothing unusual.
Next morning I went out and where I'd flushed out the hose, there was a thin white layer of toilet paper on the ground, covering every blade of grass like hardened snow!
My conclusion, (first it was not RV toilet paper), but my conclusion, "dissolving" is a hoax idea and bogus. Toilet paper does not dissolve, it breaks down into minuscule fibers that are eventually washed away, or put back into the ground where, like all paper, will eventually decay and become worm food. But right out of the holding tank? No, it's not dissolved, it's simply broken down.
Try THIS experiment? Leave the TP in a glass jar, shake it once a day until it's broken down, then pour the water through a screen strainer. The TP has gone no where! Once the water dries out, the TP is still there! Hard as a rock!