I think I found the culprit! I emptied the tank and rinsed it out with water. Then I held the other 2 lines while I blew into the 3rd line. BUBBLES! Coming from one of the other 2 lines. All this frustration over a tank leak!

I mixed up some strong epoxy and I dipped that sucker in it to seal up the holes around the tubes. Waiting for it to dry now but I don't think they're be any more bubbles. Hope that solves part (or all) of my problem.