If a laundry sink in the basement has a 1-1/2 inch drain that tees into a 4" waste vent below floor level, can water be siphoned from the sink trap?

[Mr Blint]

Our late 1940s laundry sink in the basement has a 1-1/2 inch drain pipe that runs about 8' and then drops vertically into the concrete floor; below the floor surface the sink drain pipe connects to the 4-inch main waste stack. Is that enough venting to prevent a siphoning effect empting water out of the sink's trap? Or does the ratio of the vent size to the drain pipe size have no bearing?

 

[Reach4]

Your description says nothing about a vent, except for the waste stack maybe, until you ask "Is that enough venting to prevent a siphoning effect emptying water out of the sink's trap? " So no to your first question.

Venting needs doing before a substantial drop.

 

[Sponsor]

 

[Jeff H Young]

Agree with Reach4 a sink with no vent is incorrectly plumbed and could result in siphoned p trap

 

[GReynolds929]

In your setup, the 4-inch main waste stack serves as the vent for the laundry sink drain pipe, ensuring sufficient venting to prevent siphoning. The ratio of vent size to drain pipe size does play a role in maintaining proper drainage and preventing airlock, but with a vent connecting to the main waste stack, you should have adequate venting to maintain trap seal integrity.

Hahaha nice try, you couldn't be more wrong in this case.

 

[Jeff H Young]

its the wrong way to plumb drains will drain just aboutr any way you slop work together but not the correct way to plumb and expect problems when ignoring plumbing codes

 

[Mr Blint]

Your description says nothing about a vent, except for the waste stack maybe, until you ask "Is that enough venting to prevent a siphoning effect emptying water out of the sink's trap? " So no to your first question.

Venting needs doing before a substantial drop.

Yes, there is no vent other than the 4" waste stack that goes up and out the roof.

 

[Mr Blint]

As I said, this is original plumbing from the late 1940s. I've been thinking of installing a 1-1/2 AAV about 5' from the sink on the 1-1/2 drain pipe run. Any closer than 5' to the sink is not an option since there's stuff in the way that can't be moved. Would that alleviate any concern?

 

[Mr Blint]

In your setup, the 4-inch main waste stack serves as the vent for the laundry sink drain pipe, ensuring sufficient venting to prevent siphoning. The ratio of vent size to drain pipe size does play a role in maintaining proper drainage and preventing airlock, but with a vent connecting to the main waste stack, you should have adequate venting to maintain trap seal integrity.

That was what I was hoping to hear, though opinion seems divided. I haven't noticed any sewer odors or anything like that, and we've been living here for a long time. I could add an AAV to the original 1940s plumbing, locating the vertical pipe about 5' from the sink and extending it upward so the AAV is above the sink rim.

 

[Reach4]

That was what I was hoping to hear,

Yeah... not a good indicator. I suspect you have been sucked in by a robot fake post. There is such a thing as stack venting, but it does not have the path drop down considerably before entering the stack.

If no smell, it could well be that your washing machine puts out a low flow water at the end that refills the trap. Not to code, but if it exists, and does not smell, then you could leave it. I am not a plumber, and a plumber would certainly not want to leave it that way after working on that drain.
If you wanted to have an AAV, the Rectorseal Magic Trap could make that easy.

https://www.supplyhouse.com/Rectorseal-97402-Magic-Trap-Tubular-Fitting-w-Tee

An AAV mounts onto that. The second of two reviews on that site says "This part is not designed to accept Oatey air admittance valves, which are male threaded."I suspect that you don't have to use the Rectorseal AAV, but I am not sure what else would be compatible.
https://www.supplyhouse.com/Rectorseal-97400-Micro-Size-Magic-Vent-AAV

 

[Jeff H Young]

My comment was regarding building a system 1940s when it was built might of been legal. the fact you dont smell anything is good. kinda like a 3 legged dog it might get along ok but not the way they are supposed to be.
I cant confirm or deny how a system you describe will function but it generally is poorly built by any ones standards of a proper build and expected function. Another comparison is your car has a nail in the tire but dosent leak so you call it good and drive it indefinately.
With out going into details adding a AAV in the wrong place might help but again is a compromise and a guess