I would just try and wash with water, but I think he will just have to cry it out. Try and hold him face down while he is crying so it runs out and doesn't just spread. If it gets real bad you may have to take him to ER. DO NOT try and wipe it out of his eye.
If you already have done so that may be what caused some of the swelling. That is the first instinct to do, wipe it away, so don't feel bad if you did that.
I did a real stupid thing with my first, but I am afraid all the Mommies will laugh at me if I tell the story. :0