Several people clean their tips by putting the tips in a glass bowl, cover with water about 1 inch with a couple drops of Dawn dish soap, and microwaving (yes, you heard me, microwaving!) for 3-4 minutes. I don't know who came up with that but I'm forever indebted to them! 
guy's perspective:
why bother?
they'll just stain the next time left too long in dishwater (esp. if black frosting is involved)
as long as clean and disinfected ...they still work.
Too funny. My DH is very kind in that he does the cleanup for me. (Yes, he gets BIG points for doing this) He fusses all the time about the tips. Ends up saying they're so cheap we should just throw them away and buy new each time. (Bless his heart)
I am with bobwonderbuns on the microwave trick. I got brave a few weeks ago and tried it. I'll never clean another tip any other way now........as long as there is a microwave within my reach that is.
To get the staining off you can use Bar Keepers friend. Just put a little on a small dampened cloth and it will shine them back like new. 
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