Finally came across a diagram that shows the small black hose from the top of the engine (taps into the raw cooling water) actually is supposed to tie into the exhaust manifold drain. That drain has TWO hoses; the one mentioned going to the top of the engine and the second one the blue hose that is used to drain the manifold for layup.
Since these small hoses all have the quick-connect fittings, someone in the past must have accidentally put the black hose onto the block drain. I was wondering why the two blue hoses would go to the same exhaust manifold fitting...
I would guess that the purpose of that black hose is to provide a way for air to enter the large water hose on the top of the engine (once the manifold blue hose was disconnected and drained), allowing water to drain out of that black hose and associated parts like the oil cooler and thermostat housing to prevent freeze damage.
