Black water Full valve stuck closed

The sensors that indicate level of fullness are notorious for being inaccurate because toilet paper sticks and tricks them so you may in fact be empty
Look down the open toilet and you can see into the tank
Fill to the top with water and dump again
If it really is a major clog a cheap ($10) sewer "snake" from Walmart or a home improvement store stuck down the toilet and rotated will likely fix it
Good Luck, Mike

I have had good results by opening the valve, filling the hoe with water and lifting it as high as possible. Then lowering it and repeating till it something is dislodged. This may take several efforts. also get a wand to go down the stool and break it all up from the top down so to speak.

Oh, not a cable.

Here is the good news/ bad news. I checked the grey water handle. It just spins too, but works.

I opened it to clear the area and closed it. Then removed the hose. The carefully pulled black water valve open to see if it worked. It started moving. Yeah!!

Bad news. We have a MAJOR clog as nothing was coming out. At this point we are using park restroom. Hard on wife as she is a colorectal cancer survivor with special needs and has difficulty getting around.

Any ideas beyond honey wagon?

Is this a cable valve?

If you can't get it to open, call for a honey wagon and adapt the hose down to 2" or less. Suck the tank empty through the toilet, add water suck again. Then you can replace the valve without a mess.
We do this a couple of times every year.
If the camp doesn't have one, the local septic cleaner company will.

popeyemth wrote:
Try screwing the shaft back into the valve
Turn the handle clockwise (looking at the end) while pushing in on it

and try spraying some WD-40 on the outside of the blade and maybe it will seep into the slot where its stuck.

Try screwing the shaft back into the valve
Turn the handle clockwise (looking at the end) while pushing in on it