My duck seemed to have a very good quality of life, with her regular drainings. My vet did get a lot of fluid from her. I don't recall how much, but it was shocking. Like 300+mls weekly. Near the end she suddenly stopped eating, started staring at walls, and didn't stay with her much loved flock. So I took her in for her, "goodbye procedure." For me I felt I wanted to give her as much life as I could, until she was uncomfortable.I'm thinking she may have some sort of cancer or liver issue. She is still eating, drinking, and keeping up with her flock. Her belly still has plenty of fluid in it but I won't have any extra hands here to help hold her while I drain more fluid until Monday. I guess my main concern for now is keeping her comfortable until she starts declining. Unfortunately there are no vets near me that will treat ducks, but my boss said that her boyfriend could come here to euthanize her whenever I feel it's time.
I have no judgement for you if you do it differently, I'm very fortunate to have a 24 hour avian veterinarian near me. That is just how I did it and it worked well for me and my sensitive heart.