I do not understand how a sensor that does not undergo the pressure of the water could bring the information I am looking for.
Of course the sensor must be in contact with the water column. A differential sensor connected to the tank outlet, before the shutoff valve, will accomplish the task.
A submerged/gauge sensor also needs a barometric sensor to compensate for atmospheric pressure changes.A differential sensor (two ports) doesn't need that.Leo..
Does the tank have a pipe connection at the bottom? What is the maximum depth of water in the tank?