Generally taking enemas will cause you to only lose a couple of pounds.
You will lose the weight of the poop and some water. If you have taken a lot of enemas you may actually retain that water and it becomes counter productive.
A laxative like Magnesium Citrate, or Milk of magnesia or Epsom Salt WILL take water out of your system and water is somewhat heavy, so it will cause weight loss, at least long enough to get you through if you are in a situation where you have to go through mandatory weigh in.
I'm not flat-out saying don't do it BUT: There ARE VERY REAL RISKS in getting the water out. Do your risk-benefit analysis carefully, and make sure there is enough on the line for the benefits to justify the risks, because the risks are high. Electrolyte depletion IS DANGEROUS!
In recent years we have learned that there are many normal weight or even over weight bulimics. After 20 years of associating bulimia closely with anorexia it's hard for some medical professionals to accept that, but it's what the latest science tells us.
In Middle School, one reasons I decided to start wearing shape wear that young was that I was getting bullied about my weight(Medically I was NOT even overweight, I was just built chunky and I was never "Svelt")
One girl I considered a good friend offered me a "Solution" that involved variable doses of Dulcolax. she said it worked for her.
She had no idea about my enemas, I wore a girdle to her funeral 8 years ago!!!