I would recommend AGAINST using a butt plug to stop an enema. The primary reason is that you would be trying to halt a bowel evacuation which most people typically describe as uncomfortable to begin with. The whole point of an enema is to make a movement which once started is probably going to include some muscle groups to respond in such a way as to make said movement happen despite any blockage encountered, including butt plugs. Have you ever stuck your finger in a faucet then turned it on? Your finger came out with a bunch of water. In this situation the faucet isn't made of metal, it's made of YOU. A lot more can go wrong.
If you take something like a retention enema that is not designed to be expelled rapidly you can technical do it, in the hospital they sometimes give large( 1000 ML) retention enemas with rectal Ballon catheters to help retain it,such as when treating an unconscious patient with a certain type of Encephalopathy and if it does come out "early" it has to be repeated until it lowers the ammonia level . So retaining is feasible as long as it's not a laxative or purgative formulation, such as a fleet sodium enema.
I wish people would do a little research before trying to scare people out of doing something that's pretty harmless. Retaining an enema is regularly done outside of a clinic. It's actually quite healthy to keep your insides clean. Retaining the enema is a necessary to help hardened, blocked stools soften up and break down to evacuate.
Did you know John Wayne had 20lbs+/- of compacted hardened stool in his system?
Well no wonder he walked funny , I could not tote that around .
On a brighter note they do say that rectal feeding thru retention enemas have been a success and that patients have done them for as long as 7 years and in some cases actually gained weight thru them , also in a survival situation if potable water can not be had doing enemas gets it safely into your system without any contaminants bothering you.
As long as you do not introduce air or another irritant that triggers evacuation you can hold that puppy all day long, also watch out for 'Rhoids they can trigger it if to excited, holding a washcloth or doubler firmly against the anus for a few minutes will help and then plug it.