FULL, Multiple reasons for this but FULL.
First: The less air in the tank (unlike propane tanks where folks talk about "letting the air out" (There is no air in a propane tank) Gasoline tanks DO contain AIR.. Air contains moisture (Water) which can condense out inside the tank, as the tank heats and cools (Along with the outside air) the tank will "Breath" sucking in more moisture laden air.. The less air space, the less "Breathing" it can do and the less moisture.. Of course E-xx Fuels do absorb water rather well and carry it out..
Second: I came home from Church one New Year's Eve. It was cold and I still had my Christmas Snowman up.. But he was sleeping on the job (Air-Blown inflatable) NO POWER.. A quick check showed it was not a "lcoal" problem but a neighborhood problem.
Down to the basement, get the big coiled heavy duty 8ga Cord.
Up to the back of the house, Plug the OUTLET on the cord into the INLET on the House.
Uncoil the cord as I head west (Toward the motor home) and opening a storage compartment plug into the Heavy Duty 30 amp outlet therein.
Into the Motor home and get the Gen-turi, back out and hook it up
Back inside and fire up the Generator. Listen for the CLUNK of the Transfer Switch.
Back to the basement.. CLICK and the lights come on, Click and the Furnace comes on.
Additional clicks brought up Television and Radio, Microwavfe and kitchen, More lights, Computer, modem and the like.
All those switches and cables and such, and a new Power distribution panel (I upgraded while I was at it) right about 1,000 dollars.
Warm wife... Priceless
I was glad that tank was full.