Hi bigbassman,
The handle pulls a cable that slides inside a sheath. The other end is attached to the plunger for the dump valve and is held tight by a setscrew. If the handle pulls with no resistance, the cable has come off one end or the other.
It's probably easier to check the back side of the UDC where the cable attaches to the handle. You just have to take down the rear wall of the pass through storage to see what's going on there. If that looks good, you'll have to look above the corrugated plastic (coroplast) underbelly liner.
If your Bighorn has a drop frame, you can take out the coroplast mounting screws on the corner close to the sewer outlet. You may have to take out 3 or 4 along each edge. Carefully pull down on the coroplast and move insulation out of the way. You should be able to follow the 1-1/2" gray water pipe back to the valve where it attaches to the holding tank. There's a silver plunger in the center of the valve assembly. If the cable pulled away from the plunger, loosen the setscrew a turn or two, make sure the handle in the UDC is fully closed, push the plunger in by hand, reinsert the cable, tighten.
With the coroplast mounting screws, it's much easier to taken them out with an impact wrench than with a ratcheting socket wrench or open end wrench. Also less likely to tear the head off.
