waste black water valve broke

Drill a hole slightly larger than the rod on the opposite side of where the rod is now, right in the center. Drill it about 1/4" to 3/8" into the plastic -- enough to drill through the outside of the valve body, but not too far into the gate on the inside of the valve. Take the rod that pulled out and push it into this hole to slide the gate open. You'll get some dripping out of the hole, but hardly enough to worry about. Leave the rod in the hole until your tank drains. Once the tank is drained, you can replace the valve.

Bruce