If there's a disposable diaper in your tank, it will not go through the valve or the piping leading to it until it's torn apart.
The toilets on RVs are a lot different than at home where 1.6 gallons aids in moving the poop along the pipe to the septic tank or sewage treatment plant.
Is it possible you unscrewed the rod when removing the cable?
The black water tank is NEVER intended to drain continuously. It should be allowed to fill to 3/4 capacity before dumping. If that practice isn't followed, a mound will build directly under the toilet and any water will drain away. Eventually, it will block the toilet from flushing at all. When that happens, you'll need a wand to stick down through the toilet to break it up and wash away and that's lots of trouble.
Here’s another video by Valterra, a waste dump valve manufacturer (replacement steps begin at 5:50 min):
https://youtu.be/UKSHnWhpMf0
