I did a lot of research on this and will share my results:
I just mixed some dish soap & water and then took a business card and cut it to the width of the airway and dipped the card in the soapy water and then put it in the whistle several times, turning the whistle on each side (upside down etc.) to make sure it’s everywhere. Then let it dry.
I found a webpage that said 50/50 water/dish soap with a tiny bit of alcohol. So I made up a solution of that for next time. Dish soap is good because we know it’s not toxic. Makes sense. My first batch was maybe 10 soap 90 water so 50/50 is a lot stronger. Should work better.
Also I saw one can hold the whistle like this:
http://www.flute-a-bec.com/anticondens.jpg
plug the window with your finger, and just fill up the windway with the solution and then take your finger off and let it run out. That seems easier/better. I’ll do this next time. Here are the instructions translated to English:
http://translate.google.com/translate?sl=fr&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.flute-a-bec.com%2Fmodemp.html&act=url
The other thing I read was here:
http://translate.google.com/translate?hl=en&sl=fr&tl=en&u=http%3A%2F%2Ffluteirlandaise.space-forums.com%2Fla-temperature-de-l-instrument-t33.html
It says if you blow air on your hand while your mouth is wide open and say “AHHH” it feels warm and is 31C. If you make a small hole and blow it’s cool at 23-24C. So maybe I was unintentionally blowing hot air into my whistle? For the saxophone it’s desirable to have a big open relaxed throat to get better sound.
So I did the soap and tried to think of blowing as if I was blowing through a really small hole and I had less condensation problems!! I’m going to keep experimenting and if needed redo the soap treatment with the stronger 50/50 mix. But so far so good!
I know Anticondens is an option, I may try a bottle of that.
The other advice in this thread on tonguing and putting very little of the whistle in the mouth is very useful as well.
Cheers.
PS: I also held the whistle a bit lower, I usually do about 25 degrees but holding it below 45 degrees can help the water to drain lower.