Re: Sunning stains out, should be a sticky.
Nerd alert...think of sunning diapers like putting a jaundiced/yellow baby under a bili lamp. Bilirubin is a byproduct of red cell breakdown that is found in pee, but more noticeably in poop.The liver of some babies can't handle the large amount of red cell breakdown, so they become yellow as bilirubin builds up in the blood. The uv light exposure causes the bilibrubin to break down.
Sunning pooped-on items doesn't require direct sunlight outside. Items can be sunned inside, too (near a window).
There is no hard and fast rule about how long to sun items. It may take multiple rounds of sunning depending on the time of day, how long it's left out, the cloud cover, inside or outside sunning, and food content in the poop,and the concentration of the stain, etc.