Fermented sauerkraut juice from any health food store.
Drink about 4 ounces, wait 1/2 hour, and make sure there is a clear line to the bathroom. This is an old trick used by people going on a cleansing fast in order to clear the entire digestive system.

BTW - don't let the dog get a drink of this - not even a sip. It will give them really rancid flatulence.