I've got a 1921 C Melody (see '1921 Conn Alto...' thread) that needs some serious de-mildewing action. Given that all the pads (and other soft parts) are already toast, is there any reason I shouldn't give this thing a bath in (diluted) bleach?
Thats not a good idea at all, you should call your local repair guy and ask him whats best for restoring the horn, they make stuff especially for restoring instruments and brass thats not too abbrasive or corrosive.
I have just finished a 1917 bare brass conn C mel that was covered in red/brown corrosion etc. I sprayed a kitchen surface cleaner on it then covered it in bi-carbonated soda then sprayed it again, left it in the bath (no water in it) for a few hours then washed it off. The water was dark brown and the horn was nice and shiney without the red rust anywhere.
Extreeme!! doubt it as it looks and plays superbly now i have re-padded and corked it
what i use to keep my Conn 16m clean is just a cotton cloth (formerly an undershirt) Using the sleeve off of it helps me go all the way around the horn. It sounds awesome after i polish it for about an hour