Originally Posted by docj
As enjoyable as this thread has been, I'd like to return to the OP's issue for a moment. We also can last about a week on our black tank, but we've never had an incident where anything backed up into the toilet. Usually around the seventh day one of us will notice that the toilet has begun to "burp" when it is flushed. The burping occurs when the tank level goes above the vent pipe opening. It doesn't bring up any solids and is not really much more than a signal to us that it is time to dump the tank? I think this burping behavior is pretty common; I'm surprised the OP didn't notice it long before there was any backup.
The title was really a little dramatic! It wasn't the solids that she could see in the pipe, but it was close enough for her! And yeah, she had been telling me that it "sounded" full, but I wasn't listening to her I guess!