From the sounds of it, the most likely culprit is compaction. Do the baths, and if you can, raise the temperature of the water just a couple degrees. Noting extreme, but it could help him pass the blockage. If the "phantom poop" exposes itself a bit more, while I'm not usually in favor of manhandling frogs, you may want to try and remove it manually if it's blocking the rest of the pipes. Update us when you can.