My Outback did more than 'drip' a little. Last Spring, I completely flooded the front half of the camper inside for this very reason. I finally figured it out it was the anti-syphon on the hose for the black tank flusher. It's located under my bathroom sink, very accessible. I've not replaced it yet so simply am not use it. Actually, I think my simple wand on the end of a garden hose stuck down the toilet works much better. But this is on my list of things to fix this spring. Should be an easy fix to replace it.
Looking back, I think the reason it broke to begin with, was because I failed to winterize it properly. I blew that line out with my air compressor, but I really don't think it completely cleared all the water out of the anti-syphen valve. When freezing weather hit, it broke the valve.
FYI.... mine is plastic, not metal. If metal, I don't think would have broken.