Folded back the front floor carpet.
Measured and poured 1 cup of water. Exactly 1 cup came out the bottom. Did it twice. No sign of water on the bare floor.
I feel a bit relieved.

Have a nice 4th.

 

Did the same 1 cup test to the driver's side channel. Got 90% of it back. Did it again, and got much less back, though some of it ran over to the other drain, and out the bottom.
Ran the seat forward, reached under and pulled out the rear foot heater duct exit piece. Felt underneath and there was water in the well there. Don't know if somehow it came from this second test. Don't know how the heck it could get to that spot from my test. This is the first time I've detected water under any of this half of the cabin.
Guess I'll have to undo the driver side headliner tomorrow and check out the tube. As a side thought, on either side, where would the elbows be?
Can I put back together the passenger side now, since it drains OK?

 

The elbows are at the bottom, the hoses plug into them. There really isn't much to the setup.

 

By "bottom", I'm assuming that's at the far end, an area I cannot get to. Can't imagine the purpose of elbows, at the end of the tube.
I dried out what I could, then taped up the moonroof, for good. Pretty much done with it.
Now I'll try mothballs for the chipmunks. Driving to town, I heard it scampering around in the dash. Maybe something I'll have more success with.

Thanks for your help.