Cleaning the radiator overflow
 

This may be a little OT but has anyone come up with a way to clean the inside of the radiator overflow bottle? Mine is not dirty, but stained from 304K miles and 16 years of use. I use GO5 antifreeze and it is very difficult to see it in the bottle. I have tried all the usual cleaners but none seem to work very well. Any ideas or comments? I know I could just buy a new one but that takes the fun out of mantaining these cars. I like to FIX things instead of throwing money at it.
Thanks to a great gorup.