280GE - no rear window washer squirting

[Ken C]

I just bought a 1984 280GE LWB, overall in great condition, but with a few problems that I'd like to fix -- one of which is that the rear window washer doesn't squirt. When I push the button, I hear the pump (in the engine bay) working, but nothing comes out. I've made sure the nozzle is clear; the reservoir is also full (the front window washer works fine, as does the headlight washers). There is no sign of any leaks, either.
Any suggestions where to look? how to find the hose's route through the chassis? or how to gain access to the pumps to check their output? Thanks.