One of the worst things to have happen on a long plane trip is to have to do a no. 2. Thus, just before I go to the airport, I take 2 Imodiums. Worked every time so far. Indeed, the US Bureau of Prisons does something similar for ConAir flights; they feed the cons food that binds.
The Saigon Civilian airport(Tan Son Nhut)1968, I don't think Imodium existed, and they had not yet discovered toilet paper! Government issue underwear is made with lots of fabric, when cut into small squares, never enough!