Where is the drain for the condensate drain on a 66 Skylark?

I get no dripping while the car is running, but after it sits for a while, it makes a large puddle.

I think the drain may be plugged, but for the life of me I can't find it. Looked on the firewall, took a mirror and looked behind the engine and can't seem to find it.

The manual makes no reference to where it is located.

TIA