Toilet Drains whenever Shower/Washing Machine is used

[Trisha Thornton]

I have a very old rental house. It's had loads of problems, but the newest one has me looking for help. My tenant recently got a new washing machine. Now whenever she uses the washing machine or shower the toilet drains itself. Has anyone ever had something similar happen or know what the issue could be? I've done some research and my best guess is it's a venting issue. But I think it could also be a main line clog (really hoping that's not the case) or perhaps incorrect plumbing related to the washer.