Yeah, but that is a glass of still water. Tie one on and cast it out and the dirt you can't see will get on it and the current swirling around will add to the fly collecting junk,For years I have used some stuff called Watershed. Just a tiny bit on the fly and once it dries overnight it is ready to fish.
The Loon stuff called Lochsa is proving to be real good also, it is a fly treatment that can also be used on CDC. I don't wait until I need it, instead put in on the fly once it is tied. About a month ago I tied up 3 size 16 midge parachute patterns using fine grizzly for the hackle. I treated each one with the Loon product then tossed them in a glass of water to see how long it would take them to sink. Still floating high and dry weeks later.
