Especially on tin whistles and other metal things?
I actually don’t clean them. The patina adds a certain character to an instrument. It shows that it is played and loved.
I do love it, but the problem was it look awful, scratched, stained, dented, and didn’t play that well. So the reason why I ask is because it looks like it was dumped it a vat of pitch.
Searching for “cleaning a whistle” and specifying the Whistle Forum, nets: http://chiffboard.mati.ca/search.php?search_id=1501162098&start=0
There are those who think that looks reallly good - shows it’s worth playing a lot… shows you are playing a lot… gets respect for function over ‘fashion’. 
Well not only is it stained, it has probably been in mud and all sorts of things, so I don’t want to get sick, because some of the stains are oil stains.
It would be good to know what whistle you have. Generally, I use hot soapy water. Sometimes, on brass whistles, I first polish them with Flitz and then give them a hot soapy water bath. No rocket science here. Cheers, Cyril
ummm problem made by someone a long time ago no brand