No solutions, but just some more observations in case it helps for more comparisons. I have been smoking a year and haven't had that kind of build-up. My usual smoke:
* Kingsford Charcoal, usually Minion start w/ 10-20 lit cols
* 3-4 chunks smoke wood put on at beginning (Hickory, Oak, Apple, or Cherry from BBQs Galore).
* Foiled water pan full of cold tap water
* Cold meat (or rested on counter a bit) put on at when I dump in the lit coals
* Temp "run up" of about an hour, to 230 deg. or so
* Lots of overnight, low temp smokes (220s - 230s) with bottom vents almost completely closed
I just started using a clay saucer filled with sand and wrapped with foil in place of water in the pan, and still have not seen any goo. Now I'm not trying to say my smoker's spic and span either, but it really doesn't get any dirtier than an average grill. I can't offer any answers, but at least these are some things I do if they help eliminate anything.
And I'm with whoever said scrape it out and throw it in the beans or BBQ sauce... that's true barbequer thinking.