4" DWV vertical stack with 2" WYE connections to sinks

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billjes

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I'm about to redo my two basement sinks and noticed the connections to the 4" vertical DWV stack are using 2" WYE fittings to connect two basement sinks instead of tees. Do I need to switch these to tee fittings or should I not worry about getting any restricting air flow since they are only sink drains going into a 4" stack?
 

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Tuttles Revenge

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The branch off the tee can connect in either a WYE or a San Tee. But the horizontal branch would need a vent between the drain and the trap arm of the fixture. Unless that is a vertical wet vent where no other waste comes from above.
 

Jeff H Young

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The 4 inch cannot be a vent for those lavs (wet or dry vented )unless they are re-vented up 6 inches minimum above flood rim of those sinks (out of picture) if they are vented by a differant type method , (again unseen) than thats ok too .
generally a verticle combi dosent fly on sinks but there are exceptions
 

wwhitney

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To rephrase what Jeff and Tuttle are saying:

If the sinks are relying on the stack to be their dry vent, then you need to use a san-tee at the stack. But that venting strategy only works if there is no drainage down the stack from the floor above, which is unlikely.

So when there is drainage from the floor above, the sinks should have separate venting provisions (possibly an AAV). In which case the combo at the stack is fine and perhaps preferred.

Cheers, Wayne
 

billjes

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Answer some questions. The 4" DWV stack only supports one bathroom on the 2nd Floor that has a sink, toilet and tub. The basement has a bathroom and utility sink that is shown tied to the 4" vertical stack with WYEs. Each of the two sinks in the basement have separate 2" vents about a foot away from the trap that are vented in a separate pipe going to the attic roof.
 

Jeff H Young

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Billjes its plumbed fine , could have used santees but either is fine dont see a question in post 6 ? but hope this is what you are hinting at
 

Tuttles Revenge

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Agreed. Since each branch is trapped and vented, then the method of connecting to the stack can be either fitting.
 
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