Just bought and moved into an old (1910)house. Did the 1st load of laundry and when the washer was emptying, the first floor toilet and shower drain backed up. As soon as I shut the washer off, all water drained out. Had Roto Rooter out and they snaked down through the toilet and found some roots. All was fine until yesterday, 5 days post "snaking" when it happened again. What do you think?