More commonly called black tank flush. Typically you drain the black tank until empty. Then turn on water to the flush connection. I close my black tank valve for a minute or so to let water build up in the tank, then open the valve to drain again, then repeat another time or two or three until the water is running mostly clear. Usually I see additional "solid material" come out the first time or two of draining during the flush. Just don't go off and forget you left the flush running with the valve closed.
There is most likely a antisiphon/backflow preventer valve installed internal to your RV, unless it has been removed (they are prone to failure). An external backflow prevention valve is not a bad idea.
There is no sanitizing involved in the process.
