Is there a nice way to kill my beta

Our little fish has a black cancer-ish rott looking thing spreading on his back. He already lost his top fin. He bearly eats. He looks like he hates life. I want to ease his pain, ya know? by just ending it. This sounds lame I know. it's a freaking fish, but I feel bad for the little guy. Any ideas? I don't think he can be helped, I bought beta fix stuff but I thinks it's too late.

DO NOT flush a live fish, it is a very painful death. If you want to euthanize him, get some clove oil (eugenol). Mix some in a large glass or bowl with some aquarium water in it. Make sure it's mixed in well. Put the beta in the glass. If the oil starts to go towards the top, gently mix it back in a little. In the meantime (or before you get the glass ready) put another bowl of water in the freezer. Don't let if freeze solid, just let it get a little film of ice over the top. Once your beta is knocked out from the clove oil, put him in the bowl of ice cold water. Put it back in the freezer and freese it solid. Then you can do with it as you wish (if you flush it, you might want to let it thaw a little so it'll go down). The clove oil along may not kill the fish. The freezing is what actually kills the fish, but feezing can be very painful. I've heard they can feel the ice crystals forming as they freeze (kind of like frost bite). The clove oil makes them numb, so they can't feel anything, and the freezing is then painless.

Here are things NOT to do, and why: