WHAT IF MY TOILET BACKS UP INTO MY SHOWER?
As with the toilet bubbling symptom, that usually means the main line is clogged. Since the water can't go down the clogged line, it is forced to back up out of the lowest point in the house, which can be a shower. It is best if you have a clean out on your sewer, as this makes it a lot easier to clear the line and eliminate the blockage.
WHAT DOES IT MEAN WHEN MY TOILET BUBBLES?
Normally, if you are running water down one of your sinks and your toilet begins to bubble, that means the main sewer line has a blockage. The water is simply running to the lowest point in the house, which is sometimes the toilet.