Well, I tried blowing air through the adjuster, but it's in a tight spot under the deck, so I couldn't really get the vacuum nozzle on it. So, I just severed the line right under it with the intention of re-gluing it later (I've got spare parts). This was when I realized that there was a bit of fluid in there which I drained as much as possible. I then tried blowing air straight through the severed connection. After nothing happened, I put my hand around it to form a seal, but all the shop vac did was rev up, hinting that it wasn't being productive.
I can't remember if the pump was on high, but I'll make sure I try that while blowing air through. The jets are a mixture of straight nozzles and spinners, and the air lines are configured as you described.
The tub is full, by the way. It's also filled to the proper level.
Hey, thanks for all the brainstorming you've been doing. I'm rather baffled by this issue. Are these kinds of clogs common?