Fill the water reservoir only about 3/4 of the way. The humidity is developed through the SURFACE area, and the depth is only to avoid having to fill it frequently.
The water won't spill if you tilt the Octagon20 to the flat spots as far as what would equate to about 8 o'clock one way, and 4...
I use the cartons in a Brinsea Octagon20 Advance EX incubator. The whole incubator is turned, not individual eggs. The 'bator tilts from one side to the other very slowly.