If there were moisture on the wall, and najis moisture met the wall at a lower place of the wall, would the wall become najis?
The upper [part] is not rendered najis by the lower.
The sweat of a jonob from haram is not najis, although practicing ihtiyat} (i.e. treating it as najis) is preferable, regardless of whether the sweat was perspired during intercourse or after it, the person was man or woman, if this were through zina, or anal intercourse, or that with an animal, or through masturbation.
The vapour or steam from an intrinsically najis thing such as urine or the garment that has become najis, which may form into drops on the wall or glass, is it najis?
It is considered tahir.
There are public washing machines, where everyone uses them to wash their clothes. Are these washing machines tahir? i.e. is it binding to render tahir clothes washed in those washing machines?
Everything is tahir until you are certain of it being najis.