We have been RVers longer than we've been boaters. Every RV manufacturer recommends using a holding tank treatment for the black tank; besides controlling odors, it breaks down solids and toilet paper. We always used it in the boat holding tanks, as well. We use the packets (and the type without formaldehyde) for the motorhome, and the liquid type for the boat (smaller holding tank). Available at Walmart.
For further discussion, you can use RV/marine toilet paper (rapidly dissolving), but we have always used Angel Soft toilet paper for both. It is less expensive and will break down just as fast as the RV/marine toilet paper. You want to make sure the toilet paper will break down - test it in a glass of water. The "good stuff" toilet paper is reserved for the more robust plumbing in the house.
It is also important to run plenty of fresh water into the toilet when pumping out (if your toilet is the type that can use fresh water) - it will futher reduce any "build-up" problems down the road.
This may be a crappy subject, but toilet maintenance and good usage will is important for the health of your toilet. I have been driving and maintaining commercial boats for most of the last decade... fixing the head because a guest "didn't realize you shouldn't use an entire roll of toilet paper or flush feminine products" down the head. 😱 Be frugal with your paper usage. Check that the valves are functioning properly at each pump out. If using the macerator, be sure to run some fresh water through it after you pump.
As seen in this thread, most folks have a preferred type of toilet system on a boat - my preference is the RV type (gravity always works) that uses fresh water.