Train Yourself to a Daily Routine
We're all born with a reflex to defecate a short time after we're fed, and as babies, that's what we did. With socialization, we learn to control our bladders and bowels, and we tend to inhibit this reflex. Work on reviving this innate tendency by choosing one mealtime a day and trying to have a movement after it; you may be able to teach your body to pass a stool at the same time each day. (This works better with younger people than with seniors.) By following that routine every day, whether you have to go or not, and soon it may very well become your time.