Cessna 210 fuel drip

We have a 78 Centurion which has developed a fuel "drip" underneath,
from some kind of drain tube protruding from under the fuselage on the
left side, about 12-18" behind the nose wheel opening. I am trying to
figure out what this line is coming from or is for. It is not the
fuel strainer discharge tube, nor is it the sump "quick drain".
Looking at a parts manual for the aircraft, it seems that it may be
some kind of vent or drain line coming from the fuel selector valve?
The drip is about 1 drip per minute, which keeps a wet spot about 5"
in diameter on the hangar floor.

I have discussed it with our mechanic, but only by phone since he is
60nm away, and so far he can't remember what it might be but "we would
just have to look at it".

Is anyone here familiar enough with this installation to shed some
light on it for me? Is this coming from the fuel selector? If so,
does the drip indicate the the selector needs to be serviced or
rebuilt?

Thanks!
John Clonts
Temple, Texas
N7NZ