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I am building a bathroom in my room addition,my drain pipes are all running together. I have a shower , tub, double vanity and a toilet. There is a 3 inch vent pipe behind the toilet drain and a 2 inch vent pipe off the shower drain.Do I need to run a vent pipe for the tub and vanity or will the two I have work for the whole system?

I think the 3 inch pipe is enough for both drainage system. The 3 inch vent pipe can hold all the wastes and can easily move it to the waste area.