Again, thanks for the many replies, but the only reason I just didnt
plug the center drain was becuase I didnt want water to start coming up
through sinks and toilets. Is there anything stopping the water backing
up from rising 2 stories and ruining my master bath? Or are there check
valves in place to safeguard against this sort of thing? BTW, what is
OP?

I may just pay to get a camera down there and get to the bottom of this
becuase when the center drain in the basement does back up and
overflows into the plastic tub dug into the ground, it smells of
sewage.

One other question I would really appreciate help on is the function of
a catch basin. I believe that the plastic tub I keep refering to which
catches the overflow when the center drain backs up, is sitting in the
same hole where the old catch basin used to be. Since this is no longer
outside of the house becuase of the addition, it's underneath my new
kitchen. If I were to remove this plastic tub, and a catch basin is
under there, how does it work?