Trying to figure how to pipe basement bathroom
When I remodeled my upstairs bathroom I tied into the 3"vent with a 3X2X3 vent tee and stubbed a pipe down next to the sewage riser in the basement for future use. Now that I am ready I just dug out a shovel size hole all the way around the drain riser so that I could see how deep it goes before it turns, and which direction it goes, as it leaves the house. The room that I am working in was left as a seperate room for a possible bathroom before I bought the house and the space seems satisfactory.
The house was built in the mid fifties and has cast iron drains. In the ceiling of the basement room are two 4" lead and oakum connected toilet setups with 2" shower and tub washouts connected to the 3" riser with 3X4X3 tees (one on top of the other). Underneath that there is a 3" clean-out(rusted). The 3" pipe continues until about a foot and a half below the floor where it goes into a 4" long radius elbow ending about 2' below floor and then runs diagonally (I speculate) across my room and out of the house. There may be another connection if my 1 1/2" kitchen and laundry sink drain from 45' away ties into it somewhere before it leaves the house I haven't dug that far yet.
My questions are:Will the 2" vent be sufficient for a toilet and shower? Where should I connect the vent? Can I remove the 3" cast iron from the 4" elbow 1 foot below the floor and connect a PVC 4X4X3 Tee and run 4" pipe 2' for the toilet with a 2" with trap about 5' away and tie in as a toilet wash-out and also tie in a 1 1/2" sink drain and the 2"vent (I am pushing that 2" vent aren't I)? The 3" vent above the upstairs toilets goes strait out the roof. I noticed the other sinks have their own vents, what do you think. PS I want to do this correctly but don't want to go through permit/inspections what happens If I don't?