The toilet pipe can go down almost as far as necessary before turning to the wall to be vented.
: : At some point in the life of my 75 year old house a rather poor bathroom remodel job was executed. The toilet drain ties directly into the main stack in the basement, but to put it in this location someone cut out about 3/4 of the 2 x 8 joist. Needless to say, my floor is beginning to sag. I'd like to replace this toilet with a corner unit so my knees don't hit the tub, but am concerned about clearing the new joist I plan to install. Is it possible to have the toilet drain go straight down for a foot or more before making its turn into the drain stack? Or would it be better to install a wall mount or rear commode and suffer with the lack of kneeroom (the main stack is in the wall directly behind the toilet)?