Shane,
The inside of the tank is a bit like the chamber of a revolver with a number of cylinders. The fluids are introduced through the centre of the lid, as usual, and as the level rises the fluid enters each of the chambers when it is at the bottom of the rotation. With the tank on a motorised processor the rotation is pretty swift and the film is universally soaked evenly and in quick time.
Furthermore, the walls of each cylinder are ever so slightly bowed so that fluid also cover the back of the sheets. I have had both 8x10 and 4x5 Expert drums and found them excellent (within the rationale of constant agitation).