When shooting out the back of a KC-135, assuming you are not the boom operator, you will want to lie to the right of the boom operator for best viewing of the receiver aircraft. The position to the left has reduced visibility and is therefore less desirable. Since you are actually pretty close to a large aircraft, you will want a pretty wide lens. In this case, I used a 16-85mm zoom at the 16mm setting with a Nikon D-300. You may want the boom in the photo to demonstrate aerial refueling:

Should you tire of this and prefer a more clear shot of the other aircraft, your boom might kindly fly his/her boom out of the way:

Finally, if you don’t want the viewer to even think about your aircraft, don’t include any part of it in the photo: