Here's what we do prior to putting our T-14 and gourds in the garage for winter storage:
1) Remove old nesting material and scrape out the crud from each nest compartment using a putty knife or any kind of tool that works best for you. Paint scrapers work well also.
2) Take a small bucket and mix up a weak cleaning solution of bleach and warm water (1 cup per 5 gallons). This solution will kill any residual bacteria and/or mites roaming around. Scrub each nest compartment and the exterior of the house or gourd with a brush of your choice and then flush everything with water using your garden hose. (I like to use a dust pan brush with soft bristles because it's long, easy to hold, reaches into the tight corners and conforms to all the different surfaces well).
3) Place your house or gourds on something that keeps them off the ground and let them sit outside in the sun for a day or two to dry out.
4) Repair any damage, apply a coat of paint after they have dried if needed and put them away all nice and ready for next season.
What about the debate over removing old nests every year? Click here to read more.