You can get clogs and a poop pile in the tank if there's a slow leak at the black tank outlet valve. Usually this shows up as brown water on your shoes when you uncap the sewer outlet to hook up the sewer hose. But if you're in one place for a while, you may not notice.
If you have a twist on clear adapter with blade valve hanging on the sewer outlet, you can close your tank valves, close the clear adapter valve, and see how much water accumulates in a day or two.
Here's one. This one is a bit pricey, so you may want to shop around. Also, you can buy the clear adapter and the twist on blade valve as separate devices, probably for less total.