Maybe this image will help more - Here's your typical cordis as it comes in it's sterile packaging:
See the yellow obturator site with the black O-ring labeled 'Cordis CVC?' On this picture, the portion of the Cordis extending to the left of that obturator site is the portion of the cordis that's inserted into the patient. Normally you'll probably just see that obturator site plugged with the blue cap labeled 'cap'. Alternately, you'll see a PA catheter inserted there if that's in use. The clear lumen that extends the other way from the obturator site is where you typically infuse fluids through. Another option is to insert a SLIC, which is a single lumen catheter:
This would be used instead of a PA catheter if you wanted to monitor CVP. Where I work, we also have a double lumen catheter that you can place into that obturator site giving you multiple lumens to run medicines through in case you have an issue with compatibility, since normally a cordis by itself is just a huge single-lumen CVC.
Does that help?