What about capacitance sensing? It seems like the proper application of conductors along the side of the printed tank should have a capacitance that changes with the increase in water. If they could be arranged in such a way as to produce some predictable outcome (change in frequency from LC circuit?) then we could determine height of the water. Maybe the frequency produced could be returned through the mic input instead of drip counting as a way to represent position.

BTW, I don't expect anything to come from my ramblings. When I have my peachy printer, I will be making the stepper mods myself and testing other ideas to see what is possible. :-) However, in the sprit of participation, I figured I would throw out a few ideas to see what others thought of them. I love the approach for this printer and I just can't wait to get my hands on one.