I experienced this awful mess not too long ago, it was related directly to TP. In particular, Angel Soft brand that we had used for a number of years without a problem, along with many RV folk who recommended it on many of the RV forums. Shortly prior to experiencing a major blockage in the one vacuum tank, we discovered that Angel Soft had changed their formulation and after doing the TP in a glass jar test, it failed almost as spectacularly as it blocked the vacuum tank. The blockage was a paste of TP and feces with much of the water content pulled out. There was no salvation other than removing the tank and flushing it with a hose with some mechanical loosening. I'm a retired Master plumber, it ranked up there with the top yuck-worthy experiences in my time in the trade.
I would VERY strongly discourage the use of caustics, sulfuric acid, or any chemical solution. It's bad enough with a paste of poop and paper, but caustics only compound the mess and additionally make it very dangerous. If it doesn't clear the blockage, then you've got a dangerous caustic stinky mess that will rain havoc on whatever it comes in contact with when it pops free. DON'T DO IT!!
Use a hose to flush it out. If you can manage to flush it into a normal (non-marine) toilet and flush the discharge, that's probably best, perhaps flush it into a 5 gal. bucket and then dump that in a water closet. It's just a messy job, no getting around it. Once the tank is cleared, you may consider treating it with muriatic acid to remove urinary salts that typically build up in the tank and can initiate blockage from those buildups.
Test your TP periodically. "Marine" just means more expensive, "Septic safe" is no better assurance, either. Take a wad of your potential TP, drop it in a clear container of water, let stand 10 min. or so, then shake it up. If the paper turns to a slurry, it passes. If it retains its sheet form, move to the next prospect. Use the brand that disintegrates most completely and quickly.
Patience! Good luck!