[spudstrawb]

Supposing your sensor is one of these:

The sensor consists of a pair of absolute pressure transducers, one immersed in water and the other exposed to the atmosphere above the surface of the water. The differential pressure enables water level to be computed. with an output of 0-5V DC proportional to depth, or as a serial digital data output in ASCII form

What I want to mean with "direct access to the sensor output", is having access to the 0-5V DC signal. If you have access to it, with some changes in the software, you can use for it, the ADC pin used by the solar sensor.

I only have a single pressure transducer but it looks like it might output "serial digital data output in ASCII form" rather than an output of "0-5V DC proportional to depth". I'll put my multimeter across the serial plug/socket pins and see what comes up. But the "a2055b0c0d0e0f0g0h0i" type string that I get in hyperterminal makes me think that I'm getting the "serial digital data output in ASCII form".