Nest boxes In my nest boxes I fold a feed bag to fit (nest boxes are 1 ft³ and the bag runs up the sides and the back a few inches). When a bag gets soiled; fold a new one; pop out the soiled; pop in the new. Feed bags are a nylon mesh bag. Frozen poop just peels off in below freezing temperatures and just flakes off in summer when left out in the sun to bake and dry. I have 65 trips around the sun it is the best method I have stumbled upon. Make sure the twine is removed from the open end of the bag it can get tangled around your birds.