Your amplifiers have a total gain of 2.5, is this enough? I would put a diode in series with R6 (cathode to output), so output amp runs at max gain to switch between +Vcc and -.8V. I would return R8 to to output (saves more drive current for T2 base. You op-amps can swing +ve and -ve, the -ve might destroy the output transistors
If you want to control the level in the tank, you need an on/off switch, so the pump runs "flat out" until the desired level is required. If there is too much overshoot, i.e. the tank level is too high, you need a PID controller to take into account the inertia of the pump.
Frank