Wake Vortices
The wake vortices of a large transport aircraft definitely do have the capacity to throw a fighter around. However, the effects are generally limited to the outboard wing area, and only when fairly close to the plane of the wing. Line astern is completely free of these effects. In distant history, a RAAF Hornet was 'thrown' over the tail of a B707 by the wing tip vortices (ended up almost inverted behind the opposite wing from which it started!).
Generally, when sitting in the correct tanking position behind a wing mounted refuelling pod, you will need some outboard aileron trim to counter the effects of the vortices which you are generally positioned right on the edge of.