The airport is about 18 km from Petach Tikva, which translates to about 1.5 liters of gas. I suggest filling up in Petach Tikva and forcing another 1.5 liters into the tank after the pump initially shuts off. This way the tank will be sufficiently full when you return the car and you will avoid any last minute surprises (e.g. they wont accept your credit card, etc) at the airport gas station.