Ah, makes sense. I will start doing this too. I got some black mold looking stuff in mine. I cant reach inside to clean it so I think I'll soak it in bleach a minute.
I read up on it because we got that mold too and to much of it can kill the birds. We bought a bottle brush to scrub it out. Then soak in 1/4 cup bleach to a gallon of water for an hour. Rinse several times and never use soap. The birds can taste the soap and will stop coming. I confirmed our first bird this evening. Brown with a black band on it's chest. Flew right up as I was standing on the porch then over to a Mulberry tree just outside the fence.