Hey Star, A sunny hello from Florida. Lab man was right. I played hooky and spent the day at the beach. Sarasota's beautiful this time of year. Most RR men aren't regular plumbers. They just snake out the sewer line from the house to the street or the septic tank to remove roots. If you had tree roots in the sewer line to the septic tank then ALL of your fixtures would be affected. It sounds like you have a blockage in the branch line that drains the washer. This blockage will be located downstream from the vent in the branch line. Did the RR man run a snake down from the roof vent. Because if he didn't then you will still be left with the blockage. Get a man out there to run a snake down the vent and break up the clog and send it on through. Let me know how you make out. Cheers, Tom