Recently extended our house out at ground level. Now need to put in drainage for new bathroom. I'm able to put in new soil pipe and manhole etc to run to existing soil pipe which has a vent. The distance from new toilet outlet/soil pipe to existing outlet is about 15 metres. Do I therefore need to put in a new soil stack for the new toilet? Also if I do, does it have to be inside the property with an AAV, or can I place a soil stack on the wall outside?