I sympathize with your booty blow-out situation! Bo had MAJOR tummy problems for a long time until we figured that she is allergic to all grains. We now have her on a grain-free diet and supplement her kibble with probiotics, digestive enzymes, pau d'arco tincture (for immune system support) and salmon oil. Whew!! Pyrs are pretty picky eaters & often will skip meals, so don't worry about them starving. My vet once told me that a dog can go for up to a week with only water and be fine (not that I want to test that theory, though). I also give Bo the slippery elm powder (sold at any health food store) plus canned pumpkin when she does have runny poops. It is GREAT and much easier to administer than pepto (very messy on a white dog).
Good luck!!