I agree with 2edgesword: It's probably the check valve. Mine locked up several years ago. I was going to replace it, but it's inside the kitchen cabinet and is impossible to reach (at least for a full ground, somewhat overweight man). So I bought a Camco toilet cleaning wand. I just run a garden hose through my front door and into the bathroom, attach the wand, open the flush valve on the toilet, and insert the wand into the tank. The wand has a shut-off on it, so I turn it off, go outside and open the black tank valve and turn the water on. Then I go back inside and open the shut-off valve on the wand to flush out any "debris" while the black tank is draining. Contrary to what the Jayco instruction manual says, I close the dump valve for 1-1/2 minutes to let the BW Tank partially fill. Then I open the valve and allow the tank to drain. If needed, I'll repeat that process. Since I can turn the wand and move it around inside the black tank, I've found I get a
much better flush than I ever did with the built-in black tank flush. After the second time I used it, the level indicators started working again. My wand had four "fixed" holes. A couple of months ago, I found one with a "spinner" on the end. It has both more water pressure and more water flow than the "fixed hole" wand had, so it does an even better job. Once the water coming out of the drain is clear, I shut the water off, then go inside to remove the wand from the hose, and feed the hose back out the door. With this new wand, the whole process only takes about 15 minutes.
