Digital BW, The Print

My guess as to what happened to your CIS that caused the backflow is that as
the ink level went down the "siphoning" effect "reversed" as the level got
lower. Some people have had good luck by ensuring that the ink level (not
the CIS level but the actual ink level) is kept at the same height as the
heads by raising the bottles to compensate for the lower fluid level. Make
sense?

Rick