Works in theory, but:
The flip flop will not sink enough current to turn all the segments to form an E or F. You will need a switching transisor between the Flop and the display.
The dual opamp is running open-loop as a comparitor with one input grounded, which means that it will switch very close to 0V at the other input.
Depending on the sensor, you will likely need to bias the reference input of the two opamps up at some positive voltage, like +1V so the sensor can trip it.
Better, use a schmitt-trigger hex inverter to condition the sensor signals to convert them to logic levels.
Another suggestion: it seems to me that your application really needs a third state, i.e. display a 0 to indicate that neither end point sensor is tripped. That would represent the state where the tank is either draining or filling, but has not yet reached the end points. To do that, don't use a flip-flop, just the logic levels from the sensors, like this truth table:
Code:
Top Bot Display
1 0 F
0 0 0
0 1 E
1 1 *
* never can happen, don't-care term
Two or three Nand or Nor gates would encode the two sensor signals into the three signals required to drive the seven segements.