My mathematics teacher at Highschool had been a navigator in and RAF Lancaster Bomber, during WW2.
He was once asked the same question about answering nature’s call at altitude. His reply was that while it was possible to make use of the “Elsan” chemical commode while airborne, most crew went to great lengths to avoid the process, as it was an experience few ever wished to repeat. He added, that for all the sophistication of the B17 or B24 as compared to the Lancaster, US aircrews were of the same opinion as their RAF counterparts, regarding the inconveniences of nature whilst airborne on a mission.
Regards, Uyraell.