Worst murder plot ever.
Han Solo and Shirley's plan stinks:
1) Why would you plot to commit a murder in such a public place? Hard to cover it up with all the mess and the noise and the people milling about. If the whole point of setting up the Director is to make his death look like self-defense, why stage a car crash also? Why not lure him out somewhere quiet and kill him there and then stage the accident? Why would you introduce a rogue element (Harry Caul) into the equation?
2) Why would you flush the bloody rags down the toilet instead of taking them out of the hotel the same way you took the body out? Why was the bloody toilet not investigated by the hotel?
In the end I'm left to conclude that Harry imagined the murder, the bloody toilet, and the phone call. Otherwise the story doesn't hold up.