bathroom remodel

Hi, I am doing a remodeling (adding 2 more bathrooms + 2 rooms) and my contractor is suggesting a change order (optional) to replace the current 3 inch ABS pipe to a 4 inch ABS pipe + install new cleanout. current house is 3br. 2ba and it would get upgraded to 6Br. 4Ba. - please share your...

Situation: Existing bathroom with no room to vent shower. Code for my area is IPC. PDFs and the jpgs are the same. Whichever work for you. Your thoughts on this drain line layout. Any issues with the WC drain entering the stack above the 2" drain? TIA

So why are they no longer around? I know the knee jerk answer most likely has to do with venting of fixtures and drain clogs ... but really? They were in place for years with little problem. Probably no more then any other type of bathroom drain line. Any "Old Timers" have a perspective on this...

I want to move our toilet by essentially rotating it 90 degrees. I need to move the flange slightly so that it is 12 inches from wall and has at least 15 inches of clearance on each side. What is the best method to do this so that drain and vent system are proper? The current drain goes back...