Washing machine backing up and leaking out of the top of the drain. From the main sewage line is a wye cutting to the right maybe 18 ft to another wye leading another 12ft to the P trap and then up to the washer drain. If that makes sense... at the end of the main sewage line is a wye, the straight part leading to a clean out trap and the turn leading to another wye etc. We've been in the house for 6 years and never had this problem till a couple of months ago. a local plumber came out, snake from the washer drain down (don't know how far) and looked under the house. said we need a vent line. I did some research and put in a vent line between the p trap and the sewage line (about 1ft from the p trap in the direction of the sewage line). the vent stack at the moment is coming up about 2ft into the laundry closet (i've not been able yet to connect and run it to the roof). I ran a small load of water through it and the water came back up the vent line. I just ran my 20ft hand auger in the pipes leading from the p trap to the first wye, from the first wye to the second wye, and then as far from the second wye down the main sewage line as I could. still no luck. after a few small 'test' loads of water it is still backing up.