I am roughing in a full bath in the basement. I have broken up the concret and exposed the esisting cast iron. Everything in the house has been updated and is PVC. I intend to replace the cast iron I have exposed with PVC. I have a couple of questions. For the tub drain I will connect into the old 3" drain that is burried in the floor. This is currently used for the existing washer and two floor drains. The basement is masonary block but does not lead so the floor drains are not really used. I am tapping in near where my 4" main leaves the house. I plan to eliminate the 2" floor drain and replace it with a 2" line that will act as a drain for both a future washer and a shop sink. I will also add a 2" drain for the tub and a 2" cleanout. I plan to bring the 2" drain for the tub up into an 8" x 14" x 12" deep box for the tub and leave access through the wall. My plumber told me that if the line drains within 6' of my 4" main line it does not need to be vented. Is this correct? It will be within 18" of the 4" main. Same question for the toilet. Does it need to be vented if I use 4" to connect to my main 4" stack?

Thanks