Tammy,
Since the enema that your father used seemed to be at least mildly effective, you should consider using that treatment as often as every other day.
Contrary to today's popular belief, there is no reason not to use a soap suds enema in cancer patients or in any person experiencing occasional or frequent constipation.
Far more gentle, and far, far, far more thorough than the chemical enemas, or the laxatives offered way too often, a gentle enema gives near immediate relief and may even be therapeutic for the cancer your Dad is facing.
Since we cannot leave personal contact information at this site, write to me, here, and I will try to help you with other treatment options.