humane killing of a 3" goldfish please

Hello all,

One of my goldfish has I'm pretty sure Dropsy and is in a mess. I may need
to kill it myself as it's bad enough to watch.

http://www.geocities.com/tony2kuk/fishkill.html

I read this, any thoughts please on a quick and painless way?

Any replies that might come ASAP will be greatly appreciated.

Nick Jones (UK)