Welcome! The short answer is, you can't. You should be able to clean it out and maybe scrub it with disinfectant, and spray with bleach, but unless it's smooth plastic or something similar, 'reasonably clean' is the best you can do. History about the previous flock will really help. If the property has been bird free for more than three weeks, Mycoplasma shouldn't be an issue. Marek's disease will linger for years, so if that was a problem, make sure your chicks are vaccinated, and then ISOLATED completely from the area for two to three weeks. My original coop was here when we bought the farm, but it was vacant for years, and safe. It's wood, so not very cleanable. Mary