Calls of nature cannot be ignored, an inherent problem in small aircraft. In fighter aircraft a rubber bottle was the usual item supplied, but it was exceedingly difficult to use when dressed up in flying gear and strapped in your seat.
Some older aircraft had better and more useable systems. The Avro Anson, a lovely stable steady airplane, was used for navigation and wireless operators training. It had a metal funnel fixed by the side of the door in the centre of the fuselage, a quite convenient system, with certain reservations.
The tube from the funnel went down through the bottom of the fuselage and pointed towards the rest of the plane. This tube, by accident or malicious design, was sometimes twisted round to face forwards, resulting in the contents being blown back to the detriment of the user.
On one particular training flight I, as the navigator, was busy at the table working on an exercise when I became conscious of somebody behind me. On turning round I saw the pilot, a very experienced Polish airman, standing there relieving himself.
I turned my gaze forward and my heart leapt to my mouth to see the pilots seat empty. He had trimmed the plan to compensate for moving to the rear and the plane was flying itself. My heart did not return to its proper place until he got back to his seat.
I often ponder if some innocent pedestrians below wonder where the spots of rain came from in a clear blue sky.