Vent Question for Sink Drain


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Old 04-22-05, 05:31 AM
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Vent Question for Sink Drain

Is there such a thing as having multiple vents on one drain line? When my house was switched from septic to city sewer maybe 30 years ago, they had to get creative with the kitchen sink drain. It goes straight down into the basement, makes a 90, and runs about 40 feet to where it connects to the main drain which is wall-mounted maybe 4 feet above the basement floor. The only vent on the line taps off the vertical section of pipe just above the 90-degree bend and runs up through the roof.

My wife claims the sink drains too slowly. Besides the possibility of a clog (which I'm checking out) is it possible that's because the line is so long and has only one vent? If that's the case, what would be the best way to remedy the situation?
 
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Old 04-22-05, 06:16 AM
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Most fixtures are required to have their own vent. On a kitchen sink, the vent is usually from a tee in the wall where the drain connects. The drain goes downwards and the vent goes on the upward end of the tee and then goes to the main stack. Not sure if code where you are allows them but you MAY be able to use an Air Admittance Valve. These are a vent that are installed just behind the trap on the fixture and go as high as possible under the sink. Good luck.
 
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Old 04-22-05, 08:08 AM
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You misunderstood what I said. The fixture already has a vent. It doesn't connect to a tee in the wall like you say, though, because the drain isn't in the wall. It drops from the trap straight down through the floor into the basement. There's a wye in this vertical line, and the vent connects to the "slanted" connection of the wye.

What I was trying to find out is whether a second vent is needed somewhere to help drainage simply because the line is so long. I did neglect to mention that the kitchen sink is the only fixture connected to this drain line.
 
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Old 04-22-05, 08:28 PM
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My bet is a clog. One vent is plenty. But, your vent location is not good for other reasons. It sounds like you have an s-trap which can siphon. This would allow sewer gases to come up through the sink.
 
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Old 04-23-05, 04:23 AM
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Yes, I do have an S-trap. I suspect the vent is where it is because there's no other way to run it. The house is block and stucco, so no plumbing is run inside any wall. The vent pipe runs up one corner of the kitchen, behind the cabinets. It's boxed in between the base and wall cabinets.

As you suspect, I'm pretty sure now I have a clog. I disconnected the pipe from where it connects to the sewer line and squirted water into it through a cleanout plug below the sink. Only a trickle came out the other end; after a few seconds water blew back at me. Guess I'm off to buy a snake.
 
 

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