Thanks, mad99ram.
Jayco suggested having the dealer from whom we purchased the unit take a look at the plumbing, looking for misaligned elbows. I took it in and they refused to look at the plumbing, wouldn't even look at the toilet, much less the drain lines to the black water tank. They're not too eager to do warranty work, I've discovered. Since they finally acknowledged a slide-out misalignment which they adjusted, they also suggested I bring it back for another adjustment in a few months which should be about the end of the RV season here in Virginia. I will request they look at the drain line on that toilet again, including how deep into tank the toilet drain line runs.
