We have the same tank configuration, and had the same issue. Note the word had, and if you are lucky the fix for ours will work for you. A wonderful mobile repair man in the DC area came to our aid when he used an old, flexible awning hook down the toilet and into the tank opening to detach what seemed to be a piece of holding tank insulation acting as a flap where the pipe joined the tank that caused the great waste pyramid. There clearly was an obstruction that he pulled off, one that was not detected by our home based repair guys when it was in for warranty work using a regular snake. We still need to make sure that enough water is used to flush down to the tank, but it's been 2 years and no more waste pyramid.
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