At the moment of lay, the egg has the temperature of the body of the hen, 41oC. After laying, it will cool down to the temperature of the environment, which is approximately 30oC in a litter nest, and 20oC (depending on the conditions in the house) when produced in a roll-away nest or outside of the nest, on the litter or slats.
When the egg is cooling down, the content of the egg shrinks, but the egg shell doesnt. This means that a vacuum is created inside the egg, and air is sucked through the pores into the egg. When the egg is produced in a dirty environment (a dirty nest or in the litter), bacteria will be sucked with this air into the pores, and will contaminate the eggs. These bacteria in the pores are the biggest risk for egg hygiene, as they are close to the membrane and can penetrate the egg when the temperaure goes up. Dirt and bacteria on the egg shell itself are much less of a risk, as they are far away from the membrane and the possibility to penetrate into the egg.
Of course we want to remove as much dirt as possible from the shell surface, as it is a potential risk especially during hatching, but we have to realise that the real risk is coming from the bacteria in the pores. These bacteria are very difficult to remove, as only a gas will be able to penetrate into the pores and kill bacteria. A liquid detergent, even when sprayed in a fine mist, will not be very effective against these bacteria as the pores are simpy too small for the liquid to penetrate, and the polarity of the liquid droplets will bind them to the egg shell and prevent them from penetraring further into the pores.
As the bacteria penetrate into the pores during the cooling process, it means that it is of utmost importance that eggs are produced in a clean environment. A dirty nest or litter will bring bacteria close to the egg with the risk of being sucked into the pores, even if the egg by itself looks clean.
This means that a floor egg is by definition a dirty egg, even when it is visually clean. This can be easily tested by placing clean floor eggs separatedly in an incubator. The hatchability will most probably be reduced by 20-30%, and the number of exploders (bangers) will increase. Washing or disinfection with a liquid will not really change these numbers, although it can reduce to some extent the severity of the problem.