Guideline CDC oil is made of organic and non-toxic fluids and creates a protective barrier between the fly and the water.
Just apply a small drop on the fly and do some false casts to get rid of excess floatant before you present your fly to the fish. Using a rubber band to cast off any excess floatant is even better. The bottle has a hole so you can hang it upside down. When appling just add a small portion to your fingertips and apply to fly.