washer drain backup

[bs1231]

I have a washer drain that on occasion, over the years, has backed up. Needless to say, it's a horrible mess, (slab). My little HD snake has paid off and always done a good job. The clean out is right behind the dryer. I am now remodeling the laundry and I have an idea. I am usually a diy, I've done plenty of minor plumbing but I am considering a plumber on this one and would appreciate any thoughts.
The washer is not the lowest spot in the house, or the last in line, so I know it's not roots or any major clog running to my septic tank. I believe the clog happens occasionally where one section connects to another under my slab, before the main line out.

My Question:
If I run the cleanout to the outside wall, lower than the washer drain inlet, is it possible to put some type of one way flap on it. That would (in theory)prevent the backup going out the washer drain. Then, the mess would land outside, or in a possible sealed bucket (it's under my deck). I could even stick a water alarm in the bucket as a warning...
This mess has happened 5-6 times in 11 years.

Check the picture, it's not the greatest, but I hope you can get the idea of what I 've got.

Built in 1968, Copper drain lines, looks like 2", distance to the outside wall is 'bout 20".

Thanks!

 

[Cass]

You could cut the drywall where the peice of copper goes straight up. That is
the vent, and install a clean out in the vent line above the washer. You should just snake the line 1-2 tims a year and you will never have it back up on you. Just mark your callendar.