This is a regular mistake made by many RV owners. Your black and gray water tanks along with your hose system IS NOT designed to act like a Home system. They will eventually clog up!
And that sounds like what you have, There are some things you can try such as; “kick” or move the drain hose in the hope the dried up sewage breaks up and flows out.
Otherwise, you may need to disconnect the drain hose (Yuck) and throw it away, hoping that the tank is not totally blocked also.
Then you need to regularly (weekly?) dump and drain that tank hoping to break up the dried debris over time.
Eventually, you can hope you can get back to a regular tank dumping regimen.
Also, depending on tour finances, many campgrounds have the address of specialists who will come to your camper and use a steam pressure system to clean your tank properly.