I know your fisrt thought, disgusting! I agree. The drain for my master bath has been slow for a few days. My wife just flushed the toilet and when she was washing her hands she heard a gurgking noise coming up from the tub drain. A few seconds later waste water began to come up into the tub. She said it look like toilet water of sewage.

All of this was in the same bathroom and is on the second floor. My house is 60 plus years old with PVC pluming from the tub to the main drain.

Do the toilet, sink and tub typically share the same drain? There is clearly a blockage and I would guess it is in the main line somewhere. What advice can you offer on how to best solve it DIY.