Enemas can be purgative or soothing.
If you are constipated, a purgative enema is a good way to get prompt, complete relief. Such enemas usually contain an additive to increase peristalsis. Soap, glycerin, or bisacodyl are examples. These can produce very strong cramping within 5 to 30 minutes. IMO, for a purgative enema to be really effective it must produce strong, widespread cramping. This means not just an urge at your anus to poo, but cramping throughout your bowel. Enemas like this should be retained until you feel cramping throughout your tummy. The urge usually comes in waves, followed by relaxation. Try and resist the urge waves until the enema is fully working, then release at the peak of an urge. The results should be a rapid, complete, uncontrollable poo.
A soothing enema is very different. It is usually plain, somewhat warm water, sometimes with baking soda, salt, or coffee It is taken very slowly with the recipient lying down comfortably. The slow administration is needed so as not to cause an urge to poo. After the solution is in, try to retain for at least a half hour, preferably longer. A retention aid, like a 30cc Foley catheter, about 30 Fr, is helpful. You should not need a huge retention device as a soothing enema should not cause a strong urge to poo. I find such enemas very relaxing and often doze off while retaining the solution.
Soothing enemas should be preceded by a purgative enema to clean you out of virtually all poo