There are three common household items that will help break down a hardened "poo/paper mound": Borax, Calgon, and laundry baking soda. You might try pouring a cup of one of these into the toilet, then filling the toilet with warm water. Let it sit for a couple of days, then drain and rinse. One or two applications should do the trick.
The baking soda also works well to clean the stain and bad taste out of a Thermos bottle. And unlike bleach, it won't ruin the seal.