There is nothing wrong with slaughtering chicken by means of modern machines, so long as they are sharp and they cut the throat and the oesophagus. If the machine slaughters a number of chickens at once, then it is sufficient for the person who is operating the machine to say Bismillaah just once when he starts operating it, with the intention of slaughtering them, provided that the person who is operating the machine is a Muslim or a kitaabi (one of the people of the Book, i.e., a Jew or a Christian).
Fataawa al-Lajnah al-Daa’imah (22/463).
With regard to what you say about the method of washing them, if washing them in this way takes away the blood and they come out clean, then they are taahir (pure). But if some traces of blood are left on them, then they must be washed before eating.
It should be noted that the blood which is naajis (impure) is that which is poured forth, i.e., that which flows from the chicken when it is slaughtered. As for the blood that remains in the veins after slaughtering and comes out when it is cleaned and cut up, this blood is taahir (pure) and there is nothing wrong with eating it because it is not blood that has been poured forth.
Allaah says (interpretation of the meaning):
“Say (O Muhammad صلى الله عليه وسلم): “I find not in that which has been revealed to me anything forbidden to be eaten by one who wishes to eat it, unless it be Maytah (a dead animal) or blood poured forth (by slaughtering or the like), or the flesh of swine (pork); for that surely, is impure”
And Allaah knows best.