Listen to switchable, she is very knowledgable.
I've never heard of acquired megacolon but I believe high volume enemas can cause an increase in capacity. I have a friend who, some years ago, was told he had a very high capacity colon following a barium enema, but I don't know if there was history to show enlargement over time.
For me it has always been quality, not quantity.
One of my favorite toys as been the Italian made Enteroplast, a very high quality 2500cc plastic container. I love to watch the level, part of what turns me on, and 2500cc is just fine. On the other side of the coin I had a female playmate that liked quantity, and at an Efest in Las Vegas in 2000 or 2001, managed to take over 5000cc, 2 plus Enteroplasts. There were witnesses, so this is not a fantasy. She came in second, the guy that won outweighed her by a factor of at least 3, maybe 4,
So she might very well empty a barium enema, but since they are a rarity these days we may never know.
My highest volume was just short of two 2 quart bags given to me by Mildred Burgess in her colonic clinic in Boston, I was in my 20s at the time, and while there was nothing overtly sexual it was clear Mildred loved giving enemas to me.
One of my favourite conventional bags, a Seiberling 3 quart that I have emptied a few times.