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Where does my primary stack vent go? Does it have to be at the end of the run? I have a pretty simple plumbing system. From the highest point to where the drain enters the house (lowest) I have

Tub, then bathroom sink, toilet, kitchen sink, laundry, exit to sewer.

I'd like to put my main stack as the vent on the bathroom sink. Is that ok even though tub is higher up on the run?

My code says:

Vent connection at base. Every vent stack shall connect to the base of the drainage stack. The vent stack shall connect at or below the lowest horizontal branch. Where the vent stack connects to the building drain, the connection shall be located downstream of the drainage stack and within a distance of 10 times the diameter of the drainage stack.

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You have one main stack typically. All of the plumbing drains into it and goes down. The venting for the plumbing should be above the highest drain-to-main-stack connection. The venting goes up - on a typical home it would vent out the roof. If you had the vents below then you may get water/sewage in them and your house would stink and possibly drains would not function as well. If you are more specific I can touch on how to do this right.

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  • Thanks, the clarification that the venting for the main stack should be above the highest drain to main stack is what I needed. Do you know if the main vent can be used as the P trap vent for more than one fixture (toilet, tub and vanity) if it is close enough to those fixtures? Any idea how close is close enough?
    – michael
    Commented Oct 22, 2014 at 0:05
  • @michael - Depending on the size of the pipe you can vent many different branches through one line. We use 2" PVC for bathrooms and all the fixtures vent up through that. That is generalizing but yes you can have more than one per vent-to-stack connection and that is common practice.
    – DMoore
    Commented Oct 22, 2014 at 0:29
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In answer to your question, yes it's ok to put a vent near your sink, but there should already be a vent from your main stack to your roof.

But are you asking if it's ok to have no vent except a vent near the sink? This depends on how far the other fixtures are from the main stack and other questions.

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