Richard Weir
Hello Fred, The purpose of a vented soil pipe is to allow the build up of gases, methane, to escape at a high level where the wind can carry it away. It also serves as on air input to prevent a vacuum forming when you flush the toilet. This can be done by fitting a dergo valve but it's really best to vent the stack at a high level. If you have neither I think that might be the start of your problems. It may be easy just to cut a hole in the 4" soil pipe and boss in a 50mm pipe and take this up the wall to the gutter level or carry a 4" pipe to the same position. Hope that helps. Richard.
