That was exactly what I originally considered. The issue is that I need it to be a lot bigger and without the rear moulding where the pipe would come into the fitting.
Any idea where I could get one a lot bigger and do you think I could successfully cut off the rear moulding section?
The previous owners of my house have used a vent to pass through lots of pipes such as bath waste water, that then run down next to a drain pipe of the external wall into the drain.
The issue I have is that the rain water is getting through the vent and into the kitchen behind the plaster...