I'm in favour of flushing, unless staying in a household where it is specifically requested that that not be done.
Straying a little, into anecdote for the sake of it: a late uncle of mine was notorious in the "extended" family, for being a crabby and cross-grained individual (despite his various good qualities). He prided himself on being highly logical and rational -- often, he was anything but. Circumstances caused my brother, when he was a child, to stay for a quite lengthy period of time with this uncle and his family.
Early in his stay, my brother needed to get up and use the toilet in the middle of the night; he flushed it. The following morning, our uncle -- who always had difficulty sleeping -- angrily rebuked him for flushing in the middle of the night, thus making noise. A couple of nights later, brother again needed to get up to "go", in middle of night. With uncle's words in mind, he refrained from flushing. Next morning, uncle went ballistic at him for leaving the "results" for people to find when they got up... My brother was truly gobsmacked at finding himself in this completely "you can't win" situation.