[jimcol]

If the Flush King doesn't work I think I would try a plumbers blowbag if you can snake the hose and blowbag up the black tank dump line. Thinking I could do that on our 3000rk. Not sure of the piping on the 3400. If it worked you would definately know as you can hear the water flow change as the blockage is removed. Shut the valve and turn off the water at the same time (two person job)to avoid putting pressure on the dump valve. Let us know how you come out. Jim