Secondary toilet bubbles when tub is drained. is there a simple solution to fix problem
This is an indication that the water is not that clean or the chemical for purification is too much. This should fix itself as soon the water is standardized and if not so, it is important to notify the local water company.
the pipe is clogged. you need plumbo. i dont know what it is called in your country
Clogged vent pipe