I hesitate on flagyl as it is an antibiotic and in our time of bug resistant antibiotics its best to be as sure as possible that you have something your antibiotic can treat.
For Oscar, I would do pepto, and perhaps some plain basmati rice (its long grain white rice and is much healthier). Either that, or depending on how bad the diarrhea was, I might just water down his kibble and decrease the amounts I fed him but at closer intervals, so the GI tract doesn't deal with a bunch of food all at once. IF the diarrhea is VERY severe, I'd take the dog off food entirely for at least a day, encourage water consumption (maybe even put a small amount of chicken broth or something mild but tasty into the water).
The major concern with diarrhea is dehydration, the more liquid or explosive diarrhea, the more water the dog looses from his system. The priorities are : 1st, make sure the dog is hydrated properly, 2nd, cautiously begin trying to calm the angered GI tract wich created the whole problem in the first place.
at some point as the dog's system begins to accept food again, it might not be a bad idea to add some plain, natural (without gelatin etc) yogurt as it contains acidopholus, a good bacteria wich will help the GI tract reguvinate.