Re: Tree roots in sewer line
A backwater valve only prevents water or sewage from outside from entering. If you have root blocked waste pipe and you flush a toilet inside the house you will eventually fill your soil pipe and it will exit through the lowest opening first which may be a floor drain, a lower level toilet, or even a sink. If your drain is slow in draining you should probably have the drained cleaned. The only sure way to prevent roots in the drain is to make sure there are no openings for the roots to enter. A plumbing company can usually run a camera down the drain to check for roots or openings. This can be repaired by replacing the wast pipe with new PVC or relining the pipe.
Be sure you live your life, because you are a long time dead.-Scottish Proverb