Honeywell Humidifier Leaking Near Overflow Tube
My suggestion is that you take a look at that plastic bulkhead fitting closely. The drain hose is attached and clamped in place with a nylon tie wrap. Upon inspection you will likely see that if the hose were removed the outer portion of that bulkhead fitting would screw off like a nut. The rest of the fitting projects through from the inside. There would be a flat rubber washer that seals the fitting against the inner side of the bulkhead. 

It is also possible that the fitting is one that was pressed through from the inside with catches that came through those notches and then the fitting was turned to lock it into place. In this case there should still be a rubber washer or O-ring on the inside of the drain tank.

My guess is that the rubber washer or O-ring has degraded, cracked and has thus led to the leak that you are seeing. The best bet is to replace this sealing component.

You may have an alternative that could stop the leaking on a temporary or semi permanent basis. If the tank surfaces around the fitting were nice and clean and dry without any scale or gunk it may be possible to apply a bead of silicon sealer around the fitting to stop the leaking. Success of this will depend upon if the plastic type is one that will bond well with the silicon or not.