For doing the real thing in the diaper try waiting until you naturally have to go. Then go into the bathroom and squat, without sitting and push. May take some time and practice.
As to the enema, I use a common water bottle, the cheapest I can find. I carefully insert the tip while standing, then carefully knell forward and, with the bottle straight up and down, squeeze a little water up the tail pipe. Don’t need a lot. Then stay in position until the urge is strong. I personally won’t try inserting a pad anything dry or that might lodge or come apart.