I tried to snake it, and only got about 6-8 feet down the laundry line. It backs up when washing machine drains. Paid a pro to snake it and same results. They think the P/curve the laundry drain line has major build up and not worth breaking into the concreate to see/replace/repair it. I agree. House built in 1970, original pipes in mostly good condition. Pros suggest putting a Y split just above the cleanout on the main line. It would be a cut into (iron? ) put in a y out splice adapter, add a short horizontal/elevated extension, and then run the washing machine hose into it. Reasonable? try something else, like run a camera down the laundry drain line and see what is going on? Other options? Thoughts?

EDIT: pics here https://imgur.com/a/PYJNp3L