[Mgs] Help with compressor?

[Simon Matthews]

I have a Husky brand (Home Depot own-label) compressor.  This is a
5.5HP compressor on a 40 gallon tank.

Recently, I noticed that it loses pressure when not switched on -- in
fact I can hear a hissing sound. I tracked this down to a fitting in
the side of the pipe that comes out of the tank itself. It is a little
difficult to see because I have not been able to get the cover off the
pump.

The tank has a fitting attached to it -- out of the top of this
filling is a copper hose. At one side of the fitting, a plastic hose
is attached. Opposite this plastic hose is another fitting that looks
somewhat like a bolt, except that it has a small hole in the end, out
of which air is leaking.

Does anyone has any suggestions? I don/t understand the function of
this little bolt-like fitting, so I don't really want to take it out
until I know what I am doing (or has some semblance of knowing what I
am doing).

Regards,
Simon