How do cavity nesters clean the nest?

Who woulda thunk it? I found a blog post on baby bird poop.  It turns out that it is fascinating how neatly Mother Nature has set up baby birds. The poop comes out in a little sac that the adults can hold in their beak and dump outside. The source below has a picture of an Eastern bluebird taking out the trash, so to speak.

That would certainly help in a Northern Flicker nest with no drainage or way for the nestlings to poke their bottoms over the edge of the nest (also shown in this source).

Source:

"http://10000birds.com/what-do-nesting-birds-do-with-all-that-poop.htm"