Just researched this...got the gamut of responses from:
"just throw them in there, they'll be fine"...
....to multiple detailed techniques for sanitization.
I rinsed and hand scrubbed them in 'warmer than the egg' water then dipped in a bleach solution, some I rinsed again, some I didn't.
All were developing on day 10, on day 18 now.
I know that when using an incubator we get the chance to try to refine and improve on how nature does it, but my gut reaction and my current process is to just wipe off anything massive with my finger, but otherwise incubate whatever I found on the ground. No real cleaning. They aren't cleaned in the wild, and birds are still going strong and not going extinct from lack of clean eggs.
If you want to clean, there are articles about using diluted mouthwash and things like that.
My concern was weather the bloom needed to be protected during the incubating process. This is my first time doing it as well and we have had one wet messy winter season. The eggs can be messy due to the elements.
Should say though that I sloughed off any larger chunks of poop or other stuff, lightly with a paper towel prior to spraying them. I dont think that pulling off stuff you can get your fingernail under is going to harm the protective bloom and you dont want to incubate that stuff anyway.