This is one of the controversial subject in the bird hatching world, and thery is many sometimes extreme opinions there.
Personally I am reluctant to wash eggs.
Even mine last experience hatching Guinea eggs proved washing , perhaps rather "sprinkling" does not harm them.
That what happenned:
Friend of mine gave me about 25 Guinea hen eggs she found on her 5 acres property. She does not know how old the eggs were. It was just a nest full of eggs.
Here is the thriller. Eggs were subject to daily watering by sprinkler system to the extent they got rusty from well water iron, they looked just like Welsummer eggs after this water treatment.
I incubated them anyway (could not candle them cause of heavy brown discoloration) and I hatched 15 healthy guineas out of 25 eggs, the hatch was going for 4 days! meaning some of the eggs were probably partially incubated by a hen, then more eggs were laid, meanwhile they all were watered daily with rusty water.
Draw your own conclusions regarding this.