[sbmarks3]

I your original post you talked about the tank "burping" when you flushed the toilet, and you suspected the vent line could be clogged. It looks like that very well may have been the case. Have you been able to confirm with the camera that the vent is open? You mentioned that there was a lot of debris stuck to the top of the tank which could plug the vent. Just to be safe you might consider taking a pitcher of hot water and dumping it down the vent pipe from the roof, this would insure that your vent is clear. Just a thought.