I'm currently finishing my basement, and I wanted to rough-in plumbing fixtures for a future basement. I've already got the layout, but I just need to figure out the venting for the drawing for my Permit.

I'm a novice at plumbing, and not quite sure the most efficient way. Below is my diagram I have so far with an explanation to follow.

Vent diagram

So, on the left of the image, there is an existing PVC Stack which services my kitchen and second floor bathroom. Under the floor is a 4" cast-iron drain which goes to the Municipal Sewer. Nothing else attaches to this drain beyond the stack.

My proposal, is a Shower on the left of the bathroom, vanity along the back wall, and toilet on the right side. All walls are exterior walls, so I dont' want venting and drains to be run inside them.

What I was planning, is a 4" Y, which reduces to 3" where the toilet drain meets. From there, a new 3" stack will be run up the back right corner, which will replace an existing 1.5" drain for my laundry room on the main floor. This stack will continue out through the roof of an add-on porch in the back. The vent for the vanity will run underneath the cabinets which will be installed later, up the back right corner and connect to the new stack above the laundry drain. The Shower and Toilet would be wet-vented through the vanity.

I don't fully understand all the small details of wet-venting, so I'm unsure if this will be sufficient for this bathroom. The total pipe length from the toilet flange to the vanity drain will be no more than about 7', is that too long? Will I need to find a new route for the toilet vent?

the end finished result will look similar to this:

Finished drawing

Any tips/thoughts is appreciated.

  • You pictures are ultra confusing. I could answer this if you just nixed the 3d diagrams and told me what you have and what you are putting in (in 2d).
    – DMoore
    Mar 27, 2015 at 18:48
  • @DMoore Does this help? i62.tinypic.com/e8poif.png Green will be new drains, red is the existing main drain. The new stack in the top-right corner will go up out the roof, but will have a washing machine drain tie-in as well on the main floor. In the bathroom, I'll be putting in a toilet, single sink and shower (no tub). I want to keep pipes out of the external walls, the vent in the top-right corner will be closed off, but on the warm side of the insulation/vapor barrier.
    – amace
    Mar 27, 2015 at 18:58

1 Answer 1


The new stack in the top right should connect downstream of the toilet. It can pass behind the toilet and then run parallel to the side wall to the corner. This leaves you with a wet vent via the vanity that servers the bathtub and toilet:

                     Vanity    New Stack
                       |          |
                       |          |
   Shower ------------\|          |
                       |          |
                       |   Toilet |
                       |/----     |
                       |          |
                       |          |

As a minimum, the wet vent would need to be 2” as shown on your drawing.

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