My 4" soil waste pipe exits the wall and runs several meters externally near horizontal before joiining the soil stack. I want to build a single storey extension on the back of the house with a pitched roof. The waste pipe would then exit into the roofspace of the extension. Is it possible to pass this through the pitched roof of the extension and back out to the soil stack. Could i use a pre-formed lead flashing? I have been through all the other options of moving it but cant get these to work.