A better option that household bleach is a baby bleach for disinfecting baby bottles, and rinse, rinse, rinse.
As for putting him to sleep. I use clove oil.
Take an old ice cream tub or other small container, put some tank water in and the fish. Get a jam jar and add a small amount of tank water to the jar then a few drops of the clove oil, put the lid on and shake the jar so the water turns a milky colour. Then gently pour the contents of the jam jar into the tub and cover if you do not want to watch. It only takes a few seconds for the fish to go unconscious, then he will stop breathing.