look up hysteresis. the reason you need to have an upper level sensor and a lower level sensor is to prevent the pump from starting and stopping too frequently.
as I would anticipate your project,
one upper level sensor to tell the pump to shut off and to indicate your tank is at maximum.
one lower START level to start the pump.
one EMPTY sensor to send your alarm report.
as a note, you can save the start time, the run time, the stop time, etc, in memory and if you can remote access, you can read that data.
Personally, I would add some additional sensors at the pump.
1 for water level high enough to pump
1 for no water available at pump
1 for pump running
the pins are free. the software can handle them and the sensors are very low cost.