Add a toilet to an existing drain trunk?
Looking for info on adding a toilet on slab construction.
Commercial space, looking to a add a bathroom abreast to two existing bathrooms - left to right, far right being the new bathroom. Existing bathrooms have a water closet and a sink. Got a bid of $9k to add new bathroom because the plumber says we need a dedicated line from our proposed new bathroom to the main. I say BS but I do not know the code, and, I am not sure if the existing toilet trunks are 3" or 4". I have read that ya cannot add a toilet to such an arrangement unless the new toilet is 15' away from the next toilet.
So..... what's the real deal?? Can a toilet be added by just wye-ing into the last toilet?? Can I do that if it is a 4" drain? Can I do it if it is a 3" drain?
Thanks much experts!!!