Tank should be empty when you set the CG. When you fill it up, it will be a tad nose heavy if the tank is in the nose. If you can, set the tank on the CG, however unless you have motors with pumps or install a pump (weight) this will not work. On most planes the tank is designed to be in the nose, so for the first half of your flight the CG will be towards the nose, however towards the end, it will be just right. Don't run out of fuel in a low hover!

If your brave, set the CG half full, however when the fuel gets low, it may make the plane twitchy. Or, just fly pattern stuff until half tank then cut loose when the CG shifts.

Or go to YS or gas motors with pumps.