I would like to fit a bathroom extractor fan. Problem is that there's not enough space in the soffit for the vent to exit after it's journey through the loft. I'm just wondering how long the vent pipe can be, and whether or not I could extend it to the other end of the loft so that it exits through the gable end instead? It would mean a vent pipe of around 4 metres, is this too long? I could support it every 500mm or so and introduce a drop for drainage...??