The extractor of my cooker hood and the extractor fan in my downstairs toilet are connected to two separate flexible pipes, which however are then connected through an upside down Y shaped pipe through just the one external vent pipe (this goes through the flat roof to the outside).
The problem, as you can imagine is that when the fan in the toilet is running, some of the odour comes into the kitchen, and when the cooker extractor in the kitchen is running, it smells into the toilet.
The point where the flexible pipes are connected to the upside down Y shaped pipe is easily accessible. I just wondered whether there is a way around this problem (or a sort of device out there that can be used) without having to install another separate external pipe through the flat roof. Before anyone suggest, any external vent piping can only go through the flat roof, as the walls are sandwiched between other properties.