Found these instructions for washing cocoons in website masonbeesforsale.com The website is full of valuable information

HOW TO DISINFECT BEE COCOONS

Materials: container to wash bees in, paper towels, bleach, water, measuring tools.

1. Mix a solution of cold water and bleach. Use approximately 1 tablespoon for every cup of water.
2. Place cocoons in solution and agitate (move around) until all areas of the cocoons have been exposed to solution. Let sit in solution occasionally agitating cocoons for up to 20 min. (Cocoons can be submerged longer but 10-20 minutes does the job without harming the bees).
3. Remove cocoons and pat dry with paper towels. If any of the cocoons sank in the water throw them away. Sinking cocoons indicate that the bee did not form correctly and has died.
4. Place bees in clean bee safe and store in refrigerator.

Instructions in www.masonbeesforsale.com

here is another set of instructions (somewhat different)

https://davidsuzuki.org/queen-of-green/how-to-care-mason-bees-year-round/

Today is August 30 which is 46 days until October 15

 October 15 will be cocoon harvesting day.