I cant imagine using a ferret or any animal to clean the inside of a vacuum system, let alone a scientific apparatus. These systems need to be clean and free of debris that can trap gas and water vapor or decompose and release more contaminates. Imagine if that ferret pooped and/or urinated in the middle of that 300 foot vacuum pipe. You wont be able to evacuate that pipe as those little turds will outgas and never let you reach the ultra high vacuum level needed for such experiments. Perahaps they accounted for this and used a feeding schedule to determine optimal time to let her run the pipes? It's never mentioned and another scientist developed a pigging method which instantly obsoleted the ferret.