Hi BobDavis1944,
Welcome to the Heartland Owners Forum and to the family. We have a great bunch of folks here with lots of information and all willing to share their knowledge when needed.
If you don't have time to get it repaired now, you might place one of the twist-on valves on your outlet connection. You could use the waste tank, but would not be able to dump the gray tanks until you hookup and dump the black tank. Kinda unusual that a cable comes loose, maybe have something hung in the valve. Have you tried backflushing the tank from the drain side?
Let us know what you find, it may help someone else.
Jim M