Welp. Time to give up. It's just too bad I have a bunch of hops and grains. I'll try to find a Homebrew club that will take them.
Thanks for your input.
I'm not saying anything about anyone above who has posted, but it might just be that people who have had dumpers are not willing to come out in droves and admit their mistakes or misfortune.
I had a whole run of dumpers when using old LME. Didn't figure it out until I got a fresh kit with some DME, and then repeated success with all-grain.
I've had other dumpers too, and most of them were traced back to clear mistakes that I made. Those are less frustrating than the mystery dumpers.
Brewing isn't all that hard, so you've probably just got some small things that need to be corrected.
Likewise, if you're confident of your process, then you're probably just missing a thing or two about how to put together a solid recipe.
Don't give up!