I use Ivory Soap because it it JUST SOAP No fancy perfumes or additives, just mild soap.
Serves three functions.
1) it does create a mild irritation which stimulates the muscles in the bowel wall and gets things moving.
2) It acts as a lubricant, making the poop and the bowel wall slippery makes it easier for things to come out.
3) it acts as an emulsifier, Breaks up some of the larger, harder chunks of poop and softens the rest meaning the muscles don't have to push as hard to move it out.
most of my enemas are soapsuds in warm but never hot water.
I keep a couple of bars of soap floating in tap water in the closet all the time. I shook it up well when I put it in there.
In a planned enema I will make sure I shake it well the night before. In any case, I shake it well before pouring it into the bag.
When I really want a good cleanout. I put Epsom Salt in THE FIRST ROUND ONLY. Never in the later rounds, because Epsom Salt has such a narrow therapeutic window, the difference between maximum effect and overdose is rather narrow so it pays to be careful but the first rounds is usually Epsom Salt and soapsuds in the same enema, then it's soapsuds only till a clear return.