Replace the aav. This is your easiest and most common product to fail.
Also check shower tray traps as these are often the ones to get the traps go dry if not used every other day and can easily be pulled if a large amount of soil flushed down the toilet.
Also check shower tray traps as these are often the ones to get the traps go dry if not used every other day and can easily be pulled if a large amount of soil flushed down the toilet.
