Some time ago, in hospital, I got constipated and refused to take the laxatives and stool softeners they tried to give me. IMO, they cause more problems than they solve, like excess laxative effect. Suppositories are not a great solution either, especially if you are constipated and are confined to bed, so have to use a bedpan. Bearing down is difficult.
So I asked for a plain water enema. Well, it turns out the facility did not have any enema bags. Sad but true. (how times have changed). The nurse offered to give me plain water using a Fleet bottle, emptied of solution, and I said OK. At this point it was a better option than nothing. So I got two Fleet bottles of warm water.
Nothing happened for quite a while, then, after perhaps a half hour lying on my left side, I felt a strong urge to poo and had a very swift, large, complete poo. I was quite surprised at the effect.
It seems large, highly irritating, exotic enemas are not needed to bring results. A few days later I got the same treatment, but with only one bottle of water. Same results.
After both enemas there was no residual burning or irritation. They did not work as rapidly as a Fleet, but they sure did work.