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Bigcaliber

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Quartz Hill, California
I'll be as brief as I can...One of the buildings I do maintenance in has a slow draining sink in the restroom. The men's restroom is back to back with the ladies rr. On the common wall are 3 sinks in a row on each side of the wall. My most immediate puzzle is the center and right side sinks in the men's room. The one on the left drains just fine.:) The one in the center is "slow", and the sink on the right is very slow. I pulled the P traps from all 3 and found them clear. I ran a snake gun into the wall at each sink to the clean-out, which is between the left and center sinks. Though I could not remove the clean-out plug, I know the drain, (or is it waste line?):confused:, is clear because the left drain works flawlessly. Now, (here it comes), when I stop up the drains of the other 2 sinks, and fill them to just below the overflow hole, the water will drain like the devil's chasing it. But run the water normally and they drain slow.:confused: I tried putting a hose down the vent on the roof but that nothing. In the attic, the vent pipe drops down from the roof approx. 10-12 feet to a tee. The lines from the tee go out roughly 6' where they then go into that common wall. There is a 3rd line that tee's into one of the 6' lines and goes down. On the ladies side, the sink on the right also drains slow. But it is directly across from the men's sink on the left side which drains fine. I know there is some sort of siphoning effect going on, but I have no clue as to what, how, why, or where. Any thoughts would be greatly appreciated.
 
Do the sinks have grid strainers or pop-up assemblies and are they clear.
I'm having a little trouble picturing the verbal description.The 1st vent tee is where? Does the run of the tee continue down into wall ( above what fixture ) with the branch running 6' and going down where ( above what fixtures)? Or ( reading further) is the tee on it's back with two 6' lines running horizontally in opposite directions. If so the later seems to be odd.

Can you draw a simple sketch of what you know to be true about the system. might help

I've seen grid strainers act in a similar way on brand new sinks
 
The grid strainers are clear. The vent piping...well...think of a very wide pitch fork with 3 tines pointing straight down into the common wall. The middle tine is offset a little to the left. I have no clue as to how to get a picture into the computer or sent to anyone online. The "T" is upside down, and sitting on top of an "E" rotated 90 degrees to the right so that the vertical line is horizontal and on top with the 3 horizontals now pointing down. It's as you say..."latter seems to be odd". The building was remodeled 8-9 years ago but the plumbing was not touched. I'm guessing that the vent line wasn't done right. It's a city building and suffers from "LBS"...low bid syndrome.
 
OK, I believe I got it! Is this correct? :p

Sorry for funnin' you, but I got a little lost, and decided to play on "Paint"

Mr. David is very knowledgeable and should be able to help you shortly.

Untitled.jpg
 
Something like this. If so, that makes more scince.
After re-reading your 1st description that is pretty close to how you described it.
So you do have Grid Strainers.
I have seen brand new Grid strainer drain slow especially on sinks without an over flow.
The over flow acts like a vent and draws air in while draining. Try replacing the stainer and make sure the over flow passage is clear.
Do the worst draining one 1st.
When the sink is full it drains faster due to the weight of the water and once it gets going the suction takes over.
When you run water and it goes slow it's because it gets air locked.
Try taking you finger and twirl the water on top of the grid.
The grid kind of stops the water from spinning down the drain like in a bathtub

vent.jpg
 
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