Go big or go home, Clorox Bleach solves so many little fly fishing problems! Actually a true story, some yahoo up on the Poudre River in Colorado. He'd dump bleach in the river, then wade down stream to pick up the fish.
When I started fly fishing I found a purple ESL in decent shape on the river. I picked it up and put it in my box with my other flies. When I got home I opened my box and it just reeeeeaked. I ended up throwing out the entire box and it's contents. Sniff those flies before you pick them up and add them to your collection!
I found a bottle of shrimp Smelly Jelly on the bank of the Yakima almost two years ago. I forgot that I was still carring it around until one day last summer when the carp fishing was slowing down on a hot afternoon. In desperation, I tried a carp wooley soaked down in Smelly Jelly. It didn't seem to make any difference. I was surprised. I thought carp would definely home into scent. Maybe I need a different flavor.