The tank should be completely empty when checking the CG.

On the bottom of the wing make a short line out from the fusealage at 2- 3/4 inches and another at 3 inches. Do this on both sides.

Now face the plane at the front and using your index fingers ,one under each wing, put them in the middle of the marks you made and lift. The plane should be sitting level on your finger or slightly nose down. If it is tail down then add nose weight, if it is way nose down try moving your fingers to the 2-3/4 inch mark and see if it now sits level or slightly nose down. If it is still way nose down, then add weight out near the tail

You can also try moving the reciever battery in the plane either towards the frnt if your tail heavy or closer to the tail if nose heavy. Adding dead weight (stick on lead weights) increses the overall weight of the plane, but if moving the battery brings it into the CG range then you have not added dead weight. Instead you have moved the useful weight.

See this link.

http://www.krcs748.com/introduction.htm

When checing a high wing plane, you pick it up on the bottom of the wing (gear facing down or also right side up), on a low wing you check it on the top of the wing (gear facing up or up side down)