So i removed heater core, pretty simple, cleaned things up and put it back into place, went to make the connections using the existing clamps and thought it connected/mated well. Started up & was waiting for cooler to run through the heater core, then I noticed that the connection is leaking, and leaking pretty good. Has anyone done this and can share some insight? Is there a trick on making that connection? I'm having fun mopping up the coolant now, but feel like i want to take it out again along with the tubing just so i can figure out what's wrong with that connection.

The o-rings seem ok, but I could be wrong. Should the o-rings be seated on the inside of the heater core female connection? or should it be on the pipe?