I read about these biodegradable flushable dog poop bags on Shelterrific. Fido's Flushables are made of Poly Vinyl Alcohol, which is a water-soluble material that breaks down quickly and completely and is even safe for septic.
Here's how it works: The agitation and water from flushing dissolves the bag completely, and the dog waste is treated the same way as human waste—at a septic system or sewer treatment plant. Cost is $12.95 for 50 bags.
The writer from Shelterrific recommends using the bags for regular- or small-sized dogs. I'll leave it up to your imagination to figure out why these might not be so good for large dogs...
Too messy? Or would you use this green pet product?