Be very careful using epson salt in an enema as it can seriously impact your bodies electrolyte balance. My suggestion would be to take a full bag soapsuds solution enema with the water at 103 degrees F at preparation time as a first step.
Although liquid castile soap is best, you can prepare the enama by swishing a bar of mild facial soap such as Dove in a pitcher of water until it becomes milky in color. Then pour into the enema bag.
Follow that with a salt solution enema to rinse out any remaining soap residue. Use one teaspoon of salt for each pint of water, or 4 teaspoons for a standard 2 quart bag.
If you will be needing enemas regularly, you can buy a box of pre-packaged liquid castile enema soap packets for about 10 cents each. They come in a box of 50, and you use just one for an enema. Your pharmacist can order them for you or you can purchase them online from a medical supply outlet.