My foal had scours for several days (or more, I don't remember) and I would wash his butt and put diaper rash ointment on it. That helped A LOT. His skin was getting irritated and started to peel (even the underside of his tail bone), and as soon as I started washing and applying diaper rash ointment, he has no more skin issues.
My vet said there was something better for them than the Pepto Bismol. I *think* it was liquid Imodium A-D. But would check with your vet first of course. And I don't remember the dosage. But I called the vet about it because my foal started having a little BLOOD in his diarrhea, and that freaked me out! But by the time I heard back from the vet, a day or so later, he seemed to be over the diarrhea and I didn't buy the Imodium.
My guy got both diarrhea and constipation as a foal- I remember I was out there one night about midnight, all alone because I didn't want to wake anyone up, giving him an enema because he couldn't poo! I was using straw as bedding and he was eating it and it was clogging him up. I think that was within a week or two of him being born, but I don't remember. But luckily the constipation only happened one time.