Since RVs are designed to be driven, they have blackwater (Toilet) and graywater tanks. Generally graywater isn't a problem except for odors.
Blackwater on the otherhand can be a real hastle.
The problem is that the toilet goes into a tank that's 8 to 12 inches deep and 3 foot by 6 foot across. Particularly when not moving the rig, solids tend to build up in the tank right below the toilet. This is called a pyramid blockage. Common household remedies for plugged toillets like plungers only serve to expland and solidify the pyramid base.
To prevent these solids from building up, the blackwater valve should be left closed and water and enzym treatement should be added to the tank after each emptying.
If a pyramid blockage occurs, the toilet will start backing up with the tank mostly empty.
The best tool that I've found when the toilet is completely clogged is the large drain cleaning bladder. This goes on the end of your hose (Best if combined with a short piece of hose and a shutoff valve).
You shut off the water to the rig, open the flush valve on your toilet and push this bladder into the toilet far enough to get it below the floor. You turn on the water and in seconds it has blasted a hole in the pyramid and you should see flow through the drain line. When you turn the water off, the bladder shrinks back to it's original size and the bad water in the toilet will drain away...awesome!
Once you have a hole through the pyramid block, you need to clean your blackwate tank.
The best tool for this is the swizzle. It comes in a shorter straight style and a flexible style for 5th wheels.
The last tool is if the tank is clogged at the outlet to the tank. You usually can identify this type of clog because the tank is bulging and hard from internal pressure.
For this type if clog I use a Reverse Flush Valve. You put it on the outlet to you tanks and hook your hose to it. You close the graywate valves so water doesn't go into those tanks. Open the blackwater valve and close the gatevalve on the Reverse Flush Valve. Then you hook your hose to the fitting and turn the water on. Water is then forced into the blackwater tank through the clog. Don't put much water into the tank as it's already really full. For a bad clog it might take 10 times of pushing a little water into the tank through the clog and then opening the gate valve to see if your getting solids out of the tank. Once the solids start flowing, you've unclogged your drain. Then use the swivel stick to clean your tank.