I fill-up at the Exxon next to the Boardwalk resort and make it back to the airport on "Full" and never have any problems.
If your rental company wants to see a receipt as proof that you filled-up within 10 miles of your return, you can take the Greenway (Rt. 417) towards the airport and at about the half way point take the S. Orange Blossom Trail exit, turn left and proceed a short distance to an Exxon-Mobile station on your left which is open 24 hours a day.
I think there is another service station even closer to the airport, at Lansdale Avenue (or something like that) off of Rt. 417.