If the cramps are extreme, however, I just don't wait. Another aid in retaining the water is to get into the knee-chest position when the pressure builds. This causes gravity to help hold the water in. Another method is to lie on your back, and massage the colon with both hands. Whenever you feel pressure building, or can feel a big bulge with your hands, massage around that area until the pressure relaxes.
Some people recommend rolling from one side to the other every minute or so.
The idea is that the water will flow repeatedly downhill, alternately filling the descending and sigmoid colon and then running down to the cecum. This is supposed to break up any masses in the transverse. Obviously, most people expel their enemas while seated on the toilet. This is probably not the best position for expelling water from the colon because of the need for the wide cecum to push the water up hill to the transverse, and then for the transverse to pump it back up its bag to get it to the descending. A large volume in the descending will cause the descending colon to slide down the left side and kink where it meets the sigmoid.