Firstly I'd like to thank all the experts here who are willing to help the DYSers. I am in a different trade, more commercial, but I also like to help other people do things the right way if I can. Thanks again. I am building a new home myself from the ground up. Currently just in the planning stages, I will be putting in two main floor bathrooms with almost back to back water closets common to the water wall. There will be about 4 feet between the centers of the toilet flanges. I want to place the stack in the best location and I have my first of many questions ( I'll post more questions later ) The question is can I enter the vertical 3 inch pipe with what would be like a double "Y" fitting or should I put one entry just below the other. The stack will be straight up vented and the area underneath the floor joists is a 4 foot crawl space. After the toilets are connect the 3 or what could be 4 inch drain pipe will travel in a sloped / horizontal run about 30 feet to exit the crawlspace into the main drain. Hope this question makes sense. I am in Canada. Thanks to all who reply.