correct, the fluid in the tube is coolant, it connects to the coolant vent tube there in the middle, the vertical hexagonal pipe with the bolt in it. right under the word liquid in your picture..
thanks all! so i took a bucket, lifted up my car and untwisted that white cap at the bottom of the radiator... not much liquid came out... maybe 1/2 a gallon? my radiator was originally a little above the "Full HOT" when I started, and after draining... (and 4 hours)... its 1/2 way, between the "full hot" and "full cool" markers. should I be adding more coolant?'
by the way, after much struggle (and breaking my flaring tool :'( due to the strength of the original EGR tube) I was able to rig up my modified EGR tube!
*crossing fingers that it holds up to the heat!*