Many of the most uncomfortable enemas (and laxatives) essentially put sugars into your colon and the bacteria there have a giant party and they make lots of gas, draw water into your bowl, and irritate a lot, and you poo and poo.
Examples of enemas like this are:
Milk & Molasses
Honey
Mayo (sugar and soda)
Lactulose
Sorbitol
and others. Essentially any sugary drink you can safely drink, will work.
Generally, the onset of action of these enemas is somewhat slower than many others, but the longer they are retained the more powerful their effects. A lactulose enema feels like just warm water at first, but within a half hour is impossible to hold, no matter how you try.
Some sugary things given orally have essentially the same effect, either because they are synthetic sugars that the body can't digest (sorbitol, lactulose) or because your body can't digest a natural sugar (lactose, fructose)
BTW, a big part of the well-earned laxative reputation of prunes is due to their sorbitol content.