When my washing machine drains, I can see water coming from the outside wall.. what does this mean and can I fix it by running a snake through the washing line.

Pragmatic, if the water is leaking where the drain hose meets the stand pipe snaking could very well solve your problem, but if it's leaking back in the wall then snaking and a repair of the pipe is in order. Good luck

It looks as if it is leaking from back of an outside wall becausen I can see water on the concrete when running the washing machine. I thought about snaking because it does not do it every time the machine is ran.

Snaking the line can't hurt, but if there's a leak between the walls it will have to be repaired. Washer dump a tremendous amount of water quick when draining.

I'd still check close at the stand pipe while the washer is draining, to insure the leaks not running down from the connection there. Good luck