Our home is around fifty years old and is in good shape, there seems to be a problem in the basement when the wahing machine emptys, it backs up into the laundry tub and then slowly drains away and then it gurgles or better still burps. Also there is a small bathroom nearby with a toilet, sink and shower and there is rusty water that backs up into shower with some debris as well. I have used all kinds of drain cleaners to clear this up to no avail. The pipes are cast iron of course in a house this age. Any suggestions what is causing this? One person suggested because we have an apple tree in the back yard that the roots are causing this problem, but I thought these were solid sealed pipes running into the city sewer line?
Thank you,
Redmond.

Does it have a vent pipe if so check it... it may be plugged not letting the air out there causing the burp

It probably is the roots. I have a similar problem in my own home. It might pay to give it a monthly treatment of Root Kill or similar product. It's a copper sulfate based solvent that you literally flush down the toilet. It'll kill the roots and, if done regularly, keep them from coming back.

I thought these were solid sealed pipes running into the city sewer line?
And so they are when first installed. However. Over time cracks can develop, joints can spread and roots can rnter.