This is something I've been thinking about trying. Here is some info from this website:
http://www.poultryhelp.com/uc-pfs22.html
Egg Fumigation/Disinfection
Formaldehyde gas has been used to reduce contamination on egg shells for many years. Label registration for this use was lost for several years but EPA has again registered several formaldehyde products for incubator and hatching egg fumigation. At this time no formaldehyde product has California registration for this use.
Disinfectants can be sprayed onto clean eggs during collection. Any disinfectant registered for use on hatching eggs can be used in this way. Check with local suppliers for registered materials.
Egg Washing
Some producers prefer to wash hatching eggs because residual disinfectant material remains on the eggs, which protects against recontamination.
Egg washing effectively sanitizes hatching eggs if proper equipment is available to do the job correctly. However, washing can cause contamination of eggs if the water temperature drops below recommended levels or if contamination exceeds the capacity of the disinfectant in a reservoir-type or immersion washer. Wash water must always be hotter than the eggs (recommended range, 110oF to 120oF). The washing solution must contain a detergent-sanitizer. A washer that does not recirculate water is recommended. If an immersion or reservoir-type washer is used, the water must be changed frequently; do not wash more than 200 eggs per gallon of solution capacity. Immersion time should not exceed 3 minutes, and eggs should be thoroughly dry before they are put in cases.
Disinfectants and Detergents for Egg Washing
Several disinfectants are safe for hatching-egg disinfection. Chlorine-based disinfectants have been most widely used to wash table eggs and have proved safe for hatching-egg sanitation. University of California research has shown quaternary ammonium to be an excellent sanitizer for hatching eggs. The advantages of quaternary ammonium are that it:
Is safe for hatching eggs at levels up to 10,000 ppm.
Leaves residual protection on eggs.
Is safe for equipment and personnel.
Is reasonable in cost.
Is compatible with antibiotic dipping of eggs since it is safe to use as a disinfectant in dipping solutions.
For egg washing, a solution containing 250 ppm quaternary ammonium and 10 ppm EDTA is recommended. Make the solution alkaline with sodium carbonate (a cleaning agent) to reach a pH of approximately 8.0.
Directions for preparing quaternary ammonium solutions.
Prepare the following stock solution:
10 percent quaternary ammonium disinfectant (alkyl dimethyl benzyl ammonium chloride);
0.4 percent EDTA (disodium salt) (15 grams/gallon); plus
4.2 percent sodium carbonate (Na2CO3) 160 grams/gallon).
Dilute as follows:
For egg washing, use 1 ounce stock solution in 3 gallons water.
For equipment, use 2 ounces stock solution in 3 gallons water.
Summary
The key to production of quality chicks is production of clean eggs. Proper egg sanitation will reduce transfer of bacteria from egg shells to chicks.