The most likely cause of the poo pyramid is leaving the black tank dump valve opened while hooked up to the park's sewer. Most people leave the grey tank open, but there aren't enough solids in the grey tank to worry about accumulation. The second common cause is not using enough water when flushing. Either way, the solids will collect in the bottom of the tank and build up. Some people use enzymes and Rid-X etc, but there's really no substitute for copious amounts of water and dumping only when the black tank is full. If I have to dump a partially filled black tank, I will run more water into it just before and during the dump.
And oh, BTW I learned that on this forum.