Hi can anyone advise please? The 4" underground drain from my toilet soil pipe runs into a 6" communal main sewer pipe. All pipes are plastic. I want to build a small extention housing a downstairs toilet. Can I break into the existing 4" drain by fitting a "Y" piece in order to join together or must the new pipe from the proposed toilet also go into the 6" main? Also, is there a need for an inspection chamber above the joint which would be approx 1 metre below ground level. And finally, does the new toilet connection need a vent ? hope there is someone out there that can advise. many thanks kevin