Dear srd.
This task can be done.
By measuring the hydrostatic pressure you also know the height of liquid column above the transducer as long as you know the density of the fluid. If you have changing medium types
with different densities you may have to make an adoption.
By knowing the height and diameter you are able to calculate the volume.
Please note that you only can measure the height above the sensor position. In case the tank
outlet is lower than the sensor position you have to add a fixed amount of volume.
Regards
Maikky