Thanks for the quick reply!

I did a quick search on wet-tail, and it seems to be mostly a hamster problem, so I didn't find much about mice with wet-tail. But from a quick overview of the stuff about hamster wet-tail, it doesn't sound like my mice have this. They didn't have any diarrhea that I observed, and certainly no wetness in the area of their bottom other than the prolapse itself.

As far as cleanliness of my cages, I have been cleaning a little less often (about once a week instead of every 4-5 days) since my husband broke his foot and I've been spending 4 hours/day driving him to work, coming home, picking him up, coming home. I am using the Southern States brand of pine pellets, and the cages have never been remotely close to dirty enough for the substrate to be wet (not counting an leaky water bottle incident, but that was a different cage). So while my cages aren't as clean as I'd like, I would not have thought they are dirty enough to cause this sort of problem.

Also, there were 10 (now 8) young females in a 20 gallon tank, so I don't think overcrowding would be the issue.

Any more ideas? Or if anyone still thinks it might be wet-tail or something similar, would the "dri-tail" stuff sold for hamsters work on the mice? Should I treat the rest of the colony or maybe just the ones in that particular cage? Would this treatment be safe for pregnant or nursing females?