My bathroom has a two foot 3" drain into the main 4" stack, this drains the toilet, the toilet is the highest fixture and vents into the main stack.
I am adding a shower,
I can vent the shower with a 1/1/2" existing vent about 3 feet from the toilet and within 1' of the shower trap.
Can I insert a 3-2-3 Y fitting between the the toilet and stack to serve as the shower drain or do I need to tap into the main stack after it goes vertical. This tap in will lie between the toilet and the stack, essentially before the toilet stack vent pipe.