For Christmas this year, I got (among other things) a Freeman Tweaked Sweetone C. While it is a fine whistle, I was wondering how to clean it.
What I normally do to clean my Walton’s (currently the only whistles I have are a Walton’s Irish Whistle D and the Freeman Sweetone C-that’ll change though!) is to take the head off, fill a sink with warm, soapy water, and use a dishcloth on the outside and a bottle brush on the inside. That’s for the body. For the head I usually just swish it around in the soapy water a lot to wash all the gunk out.
I wasn’t sure if the Sweetone would stand up to that, or if the material in that cavity in the whistle head would come out, or the material in the airway would come out.
Probably the safest thing would be to contact Jerry directly. He posts here regularly but you can check the
“Members” list and send a PM or e-mail.
(For what it’s worth, I haven’t cleaned any of my Freeman whistles in the several years that I’ve been playing them and they don’t appear to be gunkified.)
Best wishes.
Steve
Sent him a PM last evening. I probably won’t get a reply for several days, but hey, no rush.
Shows you how well I know the future: I didn’t expect a reply for several days, and I got one this evening!
Summary:
Since the Sweetone had a conical bore, bottle brushes or something like that wouldn’t really work too well, so basically your only option would be to swish it around to get any gunk out. If you do, be sure to shake the tube out so the water doesn’t pool. Steel can get rusty, after all.
And while the material inside the whistle head will stand up to being submersed and swished around, don’t poke anything inside the whistle head. That material never gets hard and can be easily damaged if it gets poked.
Hope this helps anyone looking for advice on cleaning their Freeman Tweaked Sweetone. 
Although the advice about the material in the whistle head would also apply (I assume) to any of Jerry Freeman’s other whistles that also have this tweak.