The pale magenta tank has been leaking. Of course, it's a major proctalgia to figure it out, because you can only tell that when there's ink in it, in which case you don't want to turn it over, and it's permanently attached to the whole batch of six tanks and to the printer, and you'd be insane to even consider detaching things or draining the ink. We found the source of the leak: the tube leading out of the pale magenta tank wasn't securely attached to the tank.
We reattached it, filled tanks as best we could, reprimed them, and after repeated nozzle cleaning, things were back to normal, we thought.
Then we found that the yellow and the pale magenta tubes were leaking.
Never again. If need be, I'll buy a printer that is built to attach bottles of ink to, but never again with the Rube Goldberg retrofitted bulk ink. The results are good, but it's a total kludge, messy as [insert favorite expletive], and a pain to transport.
UPDATE: Oh yeah, I almost forgot. The tanks have little caps for the ink input. While printing, they have to be turned so that air can get through, and when not printing, turn them to cut off air to avoid evaporation. Well... we had very carefully kept the tanks in an upright position, so ink hadn't gotten up around the cap and dried as far as I know, but when we were repriming the ink, one of the caps came apart on us. Oh, joy.