Sometimes they just can’t help themselves. 
The mucous membranes are highly folded patches of wet and sticky tissues designed to catch dust and other particles … so they do not reach your lungs.
Intelligent design is alleged to predict only optimal design while evolution predicts both close-to-optimal and sub-optimal design. Therefore, finding both optimal and sub-optimal design would tip the balance towards evolution.
Of course, someone could argue that the designer in ID is somewhat inept or doesn’t care about perfection.
Then the ultimate test is the pattern of shared derived featuers, or phylogenies.
The ultimate test of what? Intelligent design is not in opposition to common descent.
ID is not in opposition to any pattern of shared adaptions. That’s the problem.
The key here is that an intelligent designer should not be constrained to repeat past mistakes, but evolution can only work from the current form, which may not be ideal for future conditions. Therefore, human have bad knees, bad backs, blind-spots, and more, stemming from ancestry.
But that’s not the argument of the book, or at least not the section of immediate interest.
You see, it all started out as optimal design and went downhill from there. It’s like a bad creationist story without an explanation for the fall from grace.
In many mammals, smell is the single most important sense, and the structure of the entire snout was designed to optimize this sense.
Now if humans had optimally designed snouts too, then we could perhaps attribute that to common descent.
There are a variety of reasons for why we’re so susceptible to sinus infections, but one of them is that the mucous drainage system is not particularly well designed.
There is no case made in this section for common descent. None. It’s strictly a “bad design” argument.
What kind of plumber would put a drainpipe anywhere but at the bottom of a chamber?
This rearrangement produced a suboptimal design that has left us more susceptible to colds and painful sinus infections than perhaps any other animal. But as far as poor design goes, this evolutionary mishap is nothing compared to that lurks just a bit farther down in the body …
So first we need an evolutionary story to explain the optimal design. Then, since this optimal design was not inherited by common descent, we need another story for why it was lost.
That’s another reason we don’t need “bad design” arguments.
And that’s what the author gives us, a story. There are no footnotes, so whether there’s any actual science backing up the tale is not immediately apparent. There appear to be no references in the notes section at the end of the book to back up his story either.
… I haven’t been following all of this discussion (was tacking-on to TIm’s comment). What book? 
His book is called Human Errors.
I’m specifically dealing with a section of the first chapter, Nasal Sinuses That Drain Upward.
Lents says he is arguing for common descent. I say he isn’t. Or if he is it’s not like any argument for common descent that I am familiar with.
Okay, I’ll trying saying this yet again… The book is NOT an argument for evolution or against design. Some of the examples of the book, imo, do pose challenges to ID, but they are not presented and argued as such. I think the sinuses challenge the notion of ID because they are so wonkily designed, but that gets into all those messy arguments about is that a theological statement, blah, blah. The messy design of the sinuses are present in my book as a curiosity, an oddity, a quirky thing that makes for great reading. Is it evidence for common descent? I don’t know. I think it’s best understood within the framework of common descent (an accidental byproduct of the flattening of the human face), but I recognize that that’s not the same thing as being evidence for it. It is evidence for ID? Since ID theory is not my area, I certainly can’t say, but it would not be the first time that an overly Baroque biological system is presented as evidence of design. Somehow. But I guess me labelling it “overly Baroque” is me playing God again.
Or… it’s just a fun story of some weird biology in the human face. But what do I know? I only wrote the book. You are definitely in a better position to judge the intentions and purposes of every section. When you get a chance, please tell me what I was really intending when I wrote the section on childbirth - I’ve been just dying to know why I wrote all that!
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You’ve never interacted with Mung before, have you? 
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I said nothing about your intent. Did you intend the section to contain an argument for common descent?
You wrote:
Now if as i go through the book, and read section by section, and find no argument that this or that “quirk” is best explained by common descent, then what should I conclude?
We probably have a different opinion about what it means for common descent to be a better explanation.
I am talking, so far, about a specific section in the book. Are we on the same page about what section I was reading and referring to?
Where, in that section, is anything better explained by common descent? And if common descent is a better explanation, what is the alternative explanation that it is better than? The perfect design explanation? The intelligent design explanation. The what would a perfect God do explanation?