Black water tank wont empty

[garbonz]

Still a good idea to fill it half full add an enzyme cleaner (I use KO kills odor by Raritan) and let sit for several days. That may dissolve any remaining gunk.

[OldCoot]

I would put about 5-10 gal of water in the tank and about a quart of Super Clean in it and let it set overnight and then tow it home and empty it. It should be spotless. The Super Clean will do a fantastic job of dissolving any residue in the tank.

[DDC]

I had this happen once when the kids put lots of toilet paper and it was enough to block both the closet and air pipes, I accidentally freed it up by standing on the pedal and prodding the toilet paper with a stick woos and splash and it started to empty I filled and emptied it four times to clean it out, so in the end it was simple science no air in no fluids out.