National has just listed a new master rental agreement on their website. National has decided to squeeze more money from renters and not care about "customer service". This is what it says about filling up the gas tank:
(6) The fuel charge at the rate shown......Renter shall not receive a refund or credit if Vehicle is returned with more fuel than when Renter received it. If Renter purchases the Fuel Service Option, then Renter’s fuel charge shall be the per gallon (or per litre) charge multiplied by the fuel tank capacity of Vehicle rented.