"Do you have a residential refrigerator on this side..if so... maybe this is the drain."
DING, DING, DING. I believe you just answered a question I've had in the back of my mind. In mid/late 2018 I found a short tube that was profusely dripping - eventually I Assumed it was from the AC unit. However because that was the only time I ever observed it dripping I didn't really think that was the answer. My tube (coincidentally) IS located near my Res. fridge.
His description (long and blue/white) does sound like its from the fresh water tank.