Sewage valve stuck open

From your description it sounds like your seal that the blade slides between is jammed, your tank is empty, so the next step is to replace the valve. I would jack the camper up on the side that your drain is on to keep what water you have left in the tank then replace the valve. Also what I did on mine was to add grease fitting on top of the valve and pump some grease in there just to keep the blade sliding smoothly between the seals. I pump in some grease when ever the handle gets hard to operate. The grease fittings are tapered and will self tap into the plastic after a under sized hole is drilled. Hope this helps.