My Dad did say that when Mom had him use an Evac-Q-Kit in the late 1970s the Magnesium Citrate was sweetened with saccharin, which had a bitter after taste.
He felt that the extreme sweet, then the sudden extreme bitter was enough to trigger the gag reflex.
He said "There was one time when your Mom was taking the mag citrate from the Evac-Q-Kit. She knew enough to put a pillow in front of the toilet, and kneel on that pillow in case it would not stay down.
He was at the sink preparing an enema. It would have been the 3rd of the session. He didn't say, but I doubt she took it!
She was sipping it, he heard a retching sound like she was vomiting. He looked at her expecting to see her head in the toilet.
Instead she was staring straight ahead. Her cheeks bulging like a chipmunk, and she managed to re-swallow! How she did that he's not sure.
She waited several seconds, maybe a full minute, and when she collected herself, she just said, "goddamn!" and waited until she caught her breath, then held it out to see how much more was in it. It was between 1/3 and 1/4 of the 10-oz bottle. She closed her eyes, took a deep breath, took another sip and then waited for most of the bitterness to dissipate and sipped again. She DID manage to get it all down.
He never said whether she vomited later.