We bought out a 50 year old house with septic system 2 years ago. About a year and a half ago we had the septic tank drained for preventive measure. In January the washing machine started backing up when it would drain. Called Roto-Rooter and they snaked from the roof vent.

Last month we noticed that occasionally when the washing machine drains, one of the toilets will gurgle and water will be drained out. What could be the cause of this? Any suggestions or advice is greatly appreciated.