Help me ID parts of this sump pump drain system outside my house. (If I
did this right, you should be able to click on below and see photo) And
why it works.. or doesn't work the way it does...

http://photos12.flickr.com/15456715_6ea7a29b0d.jpg

It is the sump pump drain/setup outside my home (1970's cheaply built
subdivision home in upper midwest)

Ignore wiring you see, it is TV cable & AC power and not related to
drain system.

On top is the outlet from the basement, black corregated pipe connected
to the outlet from the house. It runs into top of 4" pipe which comes
up out of ground. The 2" "T" coming off to the right is where the
water has always come out, since I have owned the house (7 years)
Under that is a makeshift PVC drain that I fashioned last year, it goes
underground and drains out on lawn 20 feet from house. I did that as a
temp measure to get water from the base of house until I came up with
better plan.

When I looked down the 4" pipe that goes into the ground, I saw it went
down maybe 18" and then seemed to have an elbow and seemed to lead away
from the house foundation.

My question is this: Why does the water come out the top "T", I assume
the pipe leading into the ground was at one time a way for water to be
carried from the home... but perhaps it is plugged or something, which
causes the water to come out the top "T", which I am guessing could
have been a relif type outlet in the event the main drain is clogged.
Is that right? Is there any other reason for that pipe to exist? I
have never found any kind of outlet for that pipe out on the lawn.