Hi Enggass!
Hope you're having an awesome day, and I'm so stinking glad there was something I could offer that was of use to someone who knows all that you do!
(And we are also getting Nigerians this year; can't wait!)
Back to incubators...
Yes, the problem with the reservoirs filling beyond capacity was the January hatch period with Khaki Campbell ducklings. I definitely understand that the house was pretty dry, so to keep it as close to 65% as possible, it just kept adding water (didn't get past 62% until I added the cloths and filled the second reservoir - described below, but I don't really blame the incubator for that; the house was between 18-35%).
As a note, the incubator did successfully keep the eggs at 45% throughout the incubation without using the second reservoir or flooding; it was just the higher hatching humidity that didn't get there well enough.
Once the duckling drowned, I added wash cloths in to soak up the standing water, which is how I realized that keeping damp paper towels in could help the humidity and keep the eggs from rolling in the spaces.
I keep the second reservoir empty until hatch time (so far I haven't needed it earlier than that to maintain the humidity), but I do go ahead and stuff either a paper towel or small cloth in there so that it's ready to go and just pour warm water in on the side without having to open up the entire thing again (or take too long when I'm setting the eggs down).
Okay, I'm shutting up! I think I answered your question; if I'm missing something or can further offer anything at all (including what to NOT do), then I am more than happy to do so!
Have a wonderful evening!