I have an extension on the side of my house which is largely complete. I have a (soon to be) bathroom upstairs above my (soon to be) downstairs toilet both located on an outside wall (the gable). I have put a drain in the floor of the downstairs toilet to take the toilet waste directly out to the drain which is situated more or less directly outside the new toilet window.The problem I am wrestling with is this..... When I put the drain and inspection chamber in etc I wasnt planning on putting the bathroom upstairs as it was originally going to be a walk in wardrobe. I will now have to put a 4 inch pipe through the wall upstairs and connect it into the inspection chamber outside but where the pipe will exit is on the downhill side of the drain. I guess I will have to put a soli pipe in above the drain and connect to that but do I need to take the soil pipe directly into the chamber or can I break into a drain which joins the chamber?