re: What's the most effective way to manage a dog with diarrhea...

You can also try some plain yogurt - maybe as a puppy, he doesn't have enough good bacteria in his gut. Yogurt will help. Just give him a spoonful or two with his meals.

Also be consistent with food - switching brands or "flavors" can cause stomach issues while their system "adjusts" to the new food.

...and if that doesn't resolve it - take him to the vet.