Black Tank Flush Plugged

My black tank drains just fine. It's the black tank FLUSH that is plugged. Also, the vacuum breaker/check valve is not the problem. I suspect the suggestion to remove the flusher nozzle and clean it is what I'll have to do. Not sure how to get to the nozzle, but I bet it's not easy.

Get a "twist on" valve for the end of the dump pipe...where you hook up the drain hose to the campground's pipe. Also get a end cap for the RV drain pipe that has a garden hose fitting. The Valterra twist on valve is maybe $25, the cap with hose fitting $10? Close all the dump valves. Fill the gray tank. Open the black tank drain valve. Open the gray tank dump valve. Be sure the twist on valve is closed. Let it soak a day or 2 so the gray water may loosen the black tank plug. If not, hook a water hose the drain pipe cap, close the gray tank valve, turn on the water hose and see what happens. I would have the toilet seat cover down.

Remove the vacuum breaker/check valve and connect the hoses together, then try again. If water flows you found the problem.

Sometimes a bag of ice in your black tank will help with draining it.

I had this problem with a used unit. I lined it up with the dump and stuck a garden hose into the RV sewer drain. I then opened the dump valve and let the hose flush the valve until it cleared.

Remove the flusher from the tank. Re-drill the small holes out, check to see if water passes, if so, re-install.

Well, I tried the shop vac and it didn't work. Any other ideas?

Reverse it! Remove the vacuum breaker/check valve. The line that runs into the black tank, put a shop vac on that line. Instead of blowing, suck it backwards. You've got small bits of "something" stuck clogging those tiny little holes. Pushing 100 psi of air is only clogging it tighter. Rather than "blow", suck with a shop vac. Stick the hose of the shop vac over the line going into the tank, then tape them together so it makes a seal between the two. When it breaks free, you'll hear the difference in the sound of the shop vac. Don't use a normal vacuum sweeper that's not made for water. Because water probably will be sucked up backwards.

Anyway, try it. See if that breaks it free.