IF venting this with no AAV fixes the issue, would it be suitable to use a 4" flexi air ventilation type tube to get from the top of the stack to the vent? Either the metal or pvc ones?
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local