My black-tank flusher hook-up "looks" almost identical. I replaced it because when I attached the hose, it flooded the inside of the camper. I thought it was that check-valve leaking. Nope! Turned out, the hook-up itself was simply cracked. No matter what I could have done would have stopped the leaking. I replaced it, and no more problems. Your's could be cracked. If you have access inside the camper, swapping one of these out is very simply.