If I understand you correctly you have bypassed the trap. This condensate water is in the "negative pressure" side of draft blower. In other words with draft inducer running it is pulling air up this tube and keeping the water from running down it, that is why there is a trap . Water in the trap prevents air being sucked upwards and lets water drip downward. Reinstall the trap and see if you still get a leak
I have a seal leg using the tubing coming off of the draft blower before it dumps in the drain. This seal leg is about 1-2 inches. How much of a seal leg do think is required to seal overcome the negative draft pressure? I do not have a seal leg on the condensate draining off the heat exchanger. How much of a seal leg is required for that one? I will resinstall the factory supplied trap, but I would like to know the above answwers in case it fails. I would then build my own seal legs from 3/4 inch plastic pipe.