How to clean pipe cleaner so that it does not rust?

pipe cleaners rust when they are kept in a damp state. If you want to wash them in soap and water, you have to dry them out thoroughly when done- or else they will rust.

a better solution is to use aluminum wire inserted into a seam in the mask for maintaining shape. aluminum wire will not rust and is sold in hardware stores for hanging pictures on walls. If a single strand is not stiff enough, multiple strands of it can easily be twisted together to form a stiffer wire.

It is not expensive, and can be easily cut with a small hand tool called a diagonal cutter, also available in hardware stores.