Is one wash sufficient for Najis clothes in the washing machine, or must they be washed two or three times?

Human urine is impure by scholarly consensus. There is no specific number of washes required to cleanse impurity; a single wash that removes the substance of the impurity suffices. If the impurity is not removed by the first wash, then the washes are increased until it is gone. An exception to this is the impurity of a dog, which must be washed seven times, one of them with earth. Clothes become pure in automatic washing machines if the trace of impurity is removed from them, because the removal of impurity does not require intention.