^^^^here my take on what happens, when i take a shower I wet down then shut the nozzle off. wash my hair what little I have left then I usually rinse. the time the water is off would not let it cool hardly any, only off maybe a minute. but its cold,not warm but very cold. what I think happens when the nozzle is let to dribble is the cold water pressure is relieved so it can't some how be forced back to the hot water tank the check valves do the same thing. i'm not sure how the cold water is forced back to the tank. its got to be some plumbing magic.
Jay D.