I just built one following his post. From what I could tell from his this is what I did.
bucket #3 the catch bucket I cut about a 5" hole in the bottom and screened it just like the holes in sides of the bucket.
I believed Moot used rivets on his screen, I did not have the tools to do that so I hot glued the screen inside the bucket. on the bottom of the bucket I cut a piece of screen that covered the whole inside bottom of the bucket and then did the same for the piece that covered the sides.( cut a piece that went all the way around the inside of the bucket.)
Just a little hind sight from mine. Use the #8 hardware cloth and not window screen ( its not rigid enough) and the hot glue works but it was a pain, when I make my extra catch bucket I will buy the tools to do the rivets. Hope this helps and hopefully we can get Moot to chime in.