I would like to add a second toilet, in a new bathroom, on the back side of our main second floor bathroom. The main bath toilet currently drains into a 3 inch pvc pipe. Can I simply add the second toilet down the line from the main bath toilet? Understanding, of course that the venting would have to be proper. I read somewhere, that, if you are adding a second toilet you have to increase the size of the drain from that toilet on.