Adding bathroom - advice on vent + placement needed
I am adding a bathroom (see picture below). The current layout is that the septic is on the opposite side of the house as the bathrooms. The existing bathrooms are back to back with both toilets dumping into the 3" vent (in center of wall between 2 bathrooms, straight up through roof) as well as both sinks and bathtubs. Everything has been working well. The kitchen is also tied into this vent from a ways away, but it has a separate vent (kinda' weird that you can hear the water trickling when you are sitting on the pot and someone is doing the dishes!).
I am looking to move 1 of the toilets and 1 of the sinks about 3' away to be on the outside wall (it will still be dumping into the vent in the same location as there is room for this and still keep the necessary slope).
The new bathroom will be conected into the middle of the main sewer pipe near the 45 that is under the house (about 25' from the vent that the other bathrooms dump into). The new sink and shower will also connect there too.
My questions are:
1. When I MOVE the toilet in the existing bathroom can I still dump into the vent in the original location without needing another vent?
2. When I add the new bathroom, will I need a new vent? If yes, what is the size and location?
3. If I need to add a vent for the new bathroom, does it need to go straight up or can I run it vertical in the attic (I want all of the vents in the back of the house, not the front).
Thanks to all that answer!