Bowel movement in an open area by night:[1] All the laws of modesty that apply by a bathroom during the day apply likewise at night with exception to distancing oneself from others, in which case at night one does not need to distance himself [at all when he is in a field and the like[2]]. If there is no one else around then one may even relieve himself on the city street.[3] [However if there is an alleyway available then he is to do his needs in the alleyway.[4]] If there is someone in the area, even a gentile, it is forbidden to relieve oneself in front of him even at night, [if he is close enough to the person to be seen. This applies even if his uncovered areas cannot be seen, as since he’s being seen from close, it is immodest.[5]]
[1] Basra 3:4; Kama 3:18
[2] Basra ibid
[3] Basra ibid; In Kama ibid Admur writes “even in a public area”. Either way this implies that by day, even if no one is around one must go to an area that people are not normally found to the point that his revealed area cannot be seen from where the people are normally found. However at night he may do his needs even in an open public area if at that moment no one is around.
[4] Basra ibid
Other Opinions: Some Poskim rule that at night it is not necessary to go to an alleyway to do ones needs and he may thus do it in middle of the street even initially. [Ateres Zikeinim; P”M 3 A”A 12; Kaf Hachaim 3:36]
[5] Basra ibid