Tom,
It was a very long time ago (and I'm not sure of how the tanks were put together back then), but I think that the pickup was a flexible hose that ran from the center of the tank to the back corner. It's possible that it has curled up at the back. The bad news is that the tank will probably have to be removed to fix it.
However, you might try removing the fitting on the top of the tank and pushing a piece of stiff cable or wire into the hose to straighten it out.