What in am doing wrong? I assumed it's just the volume of the tank and then you find the weight of the water displaced. It's not working. I made sure that the diameter was changed into a radius for the volume of the sphere. Also as a sanity note, if you have a tank that sinks when it's empty it should still sink if it's full of air right?

Yeah which is why I hate it when I get these problems wrong.:) I know that has to be the answer. I can't figure out why Im not getting the right number. Here is what I am getting. 1108353.888 Newtons.

Yeah. Your equation is right. Though don't you need to divide the diamter by two to get the radius? I checked neither of those two possible solutions are correct.