Washing can be very effective, BUT it must be done properly. It is easy to not do a good job - water too hot, too much or too little disinfectant, don't get the eggs clean enough, etc. and you end up doing more harm than good. There are several members on here who disinfect eggs prior to incubating, with great success. But obviously it is not required to get a good hatch.
In this thread, post #8 explains one method of washing and sanitizing eggs. And the whole thread has some nice discussion on why certain people do or do not clean the eggs prior to incubation.
Don't wash them. You should pick eggs that are clean in the first place. Washing the eggs increases the chances of a bacterial infection in the egg during the incubation period.