Sink won't drain, think it's vent related

gorcorps

aka Brandon
Jul 18, 2004
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So I've had this problem for a couple months now, and I can't seem to fix it and I'm about out of ideas.

My kitchen sink has had problems draining for a while. It's a double sink, one side straight down in the P trap, other side a garbage disposal. It started with getting water coming up on the regular side of the sink when I started using the disposal. I shut off the disposal and the sink starts to drain, but slowly.

Over the last couple months I've tried drain-O which did nothing. I've disassembled all of the p-trap assembly to make sure that's not clogged, and it's not. The p-trap is connected to a 3ish" black PVC line with a threaded cleanout plug in the top. I've opened that cleanout and used a phone to record video of what I can see when I use the sink, and nothing seems to be backing up like this.

In fact, the sink works just fine with this cleanout open... so something seems to be screwy with my vent system. This morning I went up on the roof and found my vent pipe, and ran a garden hose down the vent to flush out any clog. I couldn't find anything, but after a while I did reach a stop point. I figured it was the end of the vent line (well, end being a turn), but maybe I'm wrong and I should have tried to keep flushing. I still have the problem and can't really use this sink without the cleanout open, which isn't a long term option as it REEKS from I assume sewer gas.

Is there anything else I should be doing or looking at? I'm about at the point where I have to call somebody that has a long borescope camera to find my problem, and I really don't want to do that for something that I'm guessing is simple.

To my knowledge I don't have a problem with any other drain in the house not working.
 

Humpy

Diamond Member
Mar 3, 2011
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There can be no vent at all and water will still drain fine.

Snake the line. The food waste has probably began to clog things up.
 

gorcorps

aka Brandon
Jul 18, 2004
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There can be no vent at all and water will still drain fine.

Snake the line. The food waste has probably began to clog things up.
Then why would it drain fine when the cleanout is open but not at soon as it's closed? If it was a simple blockage I'd see fluid backed up with the cleanout open, but I don't
 

NetWareHead

THAT guy
Aug 10, 2002
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Sounds like you have a clogged vent somewhere. Keeping the clean out open allows the drainage to occur without bubbling or slowness. The open clean out functioning in the capacity of a vent, admitting air and breaking the vacuum that holds the drainage back.

You need to figure out how far away the sink vent is from the main vent stack and where the sink vent ties in. You could rent a sewer camera and run it down the roof vent or upwards from the basement clean out. I had my sewer line camera'd and it could fit into lines 3 inch or larger but I suspect home Depot has one to rent or purchase that could inspect a typical 1.5 or 2 inch line typically used to vent a sink or bathroom.

My bathroom and kitchen vents run vertically in the walls and are accessible in the attic where they turn horizontally and to into the 3 inch main stack. I don't have any cleanouts in my vent pipes and would need to cut them to introduce a snake and some running water.
 

Micrornd

Golden Member
Mar 2, 2013
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Older vents had no covers where they protruded from the roof. It was not that unusual that "things" could crawl into those vents looking for dark spaces, water, or just a moist environment and end up dying there.
It might be best to run a snake or camera down from the roof to clear the vent as has been suggested.
Years ago we had a 8" (yes really) leopard frog hop up out of the toilet when my wife lifted the lid. Now that was a real rodeo :):confused_old::D:rolleyes:
We have a septic system so he could have only come in through the roof vent. All the roof vents are now covered similar to these - https://www.lowes.com/pd/Air-Vent-Black-Aluminum-Slant-Back-Roof-Louver/3017497
 
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Humpy

Diamond Member
Mar 3, 2011
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The vent has no relation to how well or fast water will drain. It's purpose is to break siphoning so the trap doesn't empty out and let sewer gas in the house.

The sink is open to air regardless of a clear vent, blocked vent or no vent at all.
 

gorcorps

aka Brandon
Jul 18, 2004
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I ordered an endoscope so I can start looking further down my lines. Hope it's long enough
 

NetWareHead

THAT guy
Aug 10, 2002
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Im curious about the sink draining correctly with the cleanout open. The cleanout is after the P-trap and between the main stack?

Do you ever experience gurgling in the drain or other house drains? Or for instance you flush a toilet and other drains in the house gurgle? Any siphoning of traps dry (typically you would notice a stink from a dry trap allowing gases to enter the house?)

If you fill the sink with water and let the drain out, it drains slowly? If you begin to unscrew the cleaout threaded plug, can you hear air rushing past the plug? Can you start/stop the drainage by placing your palm over the open cleanout (in effect sealing it)? Does air want to rush in or out of the cleanout when open?
 

gorcorps

aka Brandon
Jul 18, 2004
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Im curious about the sink draining correctly with the cleanout open. The cleanout is after the P-trap and between the main stack?

Do you ever experience gurgling in the drain or other house drains? Or for instance you flush a toilet and other drains in the house gurgle? Any siphoning of traps dry (typically you would notice a stink from a dry trap allowing gases to enter the house?)

If you fill the sink with water and let the drain out, it drains slowly? If you begin to unscrew the cleaout threaded plug, can you hear air rushing past the plug? Can you start/stop the drainage by placing your palm over the open cleanout (in effect sealing it)? Does air want to rush in or out of the cleanout when open?

My setup is sort of similar to this, but not as many bends and mine has a proper P-trap:

https://www.askmehelpdesk.com/attac...p-could-slab-underground-kitsink_plumbing.jpg

My P-trap goes straight to the main stack with a threaded cap similar to what is seen on the bottom of this picture. When that cap is tight, I get drainage problems... when it's loose or off it seems to fix itself. It started with months of this particular sink gurgling, but only after water was run through it or the dishwasher was draining. I don't hear gurgling anywhere else, and I don't think there was gurgling coming from this sink without water flowing through that line.

I'll have to check if I hear any air rushing in or out when it's draining, I didn't think about that.
 

WHAMPOM

Diamond Member
Feb 28, 2006
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A do-it-yourself plumbing book will show you proper venting. If your sink is similar to the photo, I see no vent line there at all. Does your sink have a vent line?
 

Scarpozzi

Lifer
Jun 13, 2000
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Squirrels and birds and other rodents can get in those vent lines and clog them up. The reason you don't have this problem in other rooms is because all the vents are independent and a fixture is usually a minimum of 6' away from a vent or stack.

I'd probably just get a good flat tape snake (they tend to be more rigid) and feed that down from the roof until you hit resistance....and when you do listen to see if what you're hitting sounds like black ABS pipe or something organic... The problem with vent lines though, is that they can follow some tight bends. Water lines, when horizontal follow combination wyes or, a wye plus a street 45 to allow drain snakes to clean more effectively. You may hit closet 90's that are tight or other fittings that won't allow the snake to pass. We had someone snaking a drain at my place of employment a few years back....they hit a cast iron 45 in a really old plumbing stack and poked a hole in it with a drill auger. Be careful so you don't damage the pipes...
 

gorcorps

aka Brandon
Jul 18, 2004
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What did you find out?

That I should have bought a better scope =P

I haven't got back onto the roof since I bought it to check the vent in more detail. I scoped the cleanout under the sink and didn't find anything in there other than a thin layer of goo from the garbage disposal (which I expected). Since I'm able to get the sink to drain and only have to deal with the smell it's not high on my summer priority list, but it'd be nice to get it figured out before it gets cold.
 

Pick2

Golden Member
Feb 14, 2017
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Symptom: slow draining in the kitchen sink only.
Most likely cause is a grease clog. Most likely spot is where the drain goes below ground level because the temp usually drops to ~52 F at that point.
Boil a large pot of water , or two , and pour it down the sink. If it clears or improves at all , it's grease.
and/or get a 20' or longer hand snake and get at it :)
Could also be something solid , a drinking straw or twig , that got wedged in the pipe and has collected other debris. A snake should dislodge that also.
HTH
 

gorcorps

aka Brandon
Jul 18, 2004
30,739
451
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Symptom: slow draining in the kitchen sink only.
Most likely cause is a grease clog. Most likely spot is where the drain goes below ground level because the temp usually drops to ~52 F at that point.
Boil a large pot of water , or two , and pour it down the sink. If it clears or improves at all , it's grease.
and/or get a 20' or longer hand snake and get at it :)
Could also be something solid , a drinking straw or twig , that got wedged in the pipe and has collected other debris. A snake should dislodge that also.
HTH

Thanks, but did you get to the part where the sink drains fine as long as I crack open the drain line? If there was a physical clog, that wouldn't make a difference.
 

Pick2

Golden Member
Feb 14, 2017
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I did catch that part. Your vent is probably plugged , but so is your drain. I don't think just a plugged vent would cause slow draining of water.
I don't know the topology of your drain , so let me just take a guess. You probably have a horizontal pipe which Ts into another pipe , up that pipe is vent and down is the sewer. you might have a clog before or at the T. The horizontal pipe is filling with water and with the cleanout plug in , it's pressurizing the pipe , slowing the sink drain till it equalizes. with the cleanout plug off , you just fill the pipe ,careful that you don't put enough water down the sink fast enough that it overflows the cleanout.

That's My guess , anyhow. Without "Boots on the Ground" :) it is all I have :)
 
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piasabird

Lifer
Feb 6, 2002
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Even if you have a disposal on the sink, it will not grind up everything good enough. Things like greasy foods can clog up the pipes. If you live in a house, I would first wonder if tree roots are getting into your drain pipes outside. You probably need a rotor rooter service done to clean out your drains. When it comes to owning a house, whatever can go wrong will. Trees can be a pain. It helps to know how the drains empty to the outside to know how to attack this problem. Take cleanout below the sink apart and see if that is clogged up first. It may have water in it so have a bucket handy. If that is clean some point down the drain may also be backed up like a bathroom sink or tub.
 
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shortylickens

No Lifer
Jul 15, 2003
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In your case, I think its time to call a plumber.
My skills are limited to snaking and boiling.
 

Steve Gracia

Junior Member
Jun 14, 2018
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The vent has no relation to how well or fast water will drain. It's purpose is to break siphoning so the trap doesn't empty out and let sewer gas in the house.

The sink is open to air regardless of a clear vent, blocked vent or no vent at all.
This isn't true. The P-Trap yes is suppose to stay filled with water to prevent sewer gases from coming inside. Once air vent pipes are clogged, negative pressure is created which can definitely slow the water flow or completely clog the pipes. At the same time not allowing the ordor and gases to escape and not allowing the positive pressure from clean to flow through. Same concept as sticking a straw into any liquid, filling it up and then capping one end with your finger. What happens? The liquid with stay in the straw until you remove your finger. Having clogged air vents with keep creating clogs in the pipes alot more and will have to snake them more then usually. Just remember, gravity always wins. So keep those air vents clear.
 

Humpy

Diamond Member
Mar 3, 2011
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Same concept as sticking a straw into any liquid, filling it up and then capping one end with your finger.

It's not the same concept. A straw has two ends. The plumbing system has three; the vent, the sink hole, and the sewer. In general, capping the vent still leaves two openings and allows water to flow.

Happy one year anniversary to this thread! I hope the OP hasn't drowned in backed up sewer water by now.
 

Steve Gracia

Junior Member
Jun 14, 2018
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It's not the same concept. A straw has two ends. The plumbing system has three; the vent, the sink hole, and the sewer. In general, capping the vent still leaves two openings and allows water to flow.

Happy one year anniversary to this thread! I hope the OP hasn't drowned in backed up sewer water by now.
This is true. Water will still flow. But not smoothly. Ignoring the vent holes creates more clogged pipes meaning more times you need to snake the drains. Having that third open creates more air flow and pressure. Especially since the force of gravities direction is towards the earth. Earths mass pulls everything towards it. Not side to side. But everything works great here. Snaked all the pipes and vents and then hydro pressure washed them.
 

NRLY

Junior Member
Jan 8, 2019
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It's not the same concept. A straw has two ends. The plumbing system has three; the vent, the sink hole, and the sewer. In general, capping the vent still leaves two openings and allows water to flow.

Happy one year anniversary to this thread! I hope the OP hasn't drowned in backed up sewer water by now.


I hate to say it but as Steve Gracia accurately pointed out, you are simply WRONG.

"When the vents in your plumbing drain system are clogged, the flow of water can slow down or stop altogether. The vents admit air to replace the vacuum of rushing water, and when they are completely blocked, the effect is much the same as covering the end of a full drinking straw with your finger. The water stays where it is."

If you still want to dispute it, quit spreading misinformation and simply ask a professional plumber or take the time to read and educate yourself.
 

Greenman

Lifer
Oct 15, 1999
20,471
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I hate to say it but as Steve Gracia accurately pointed out, you are simply WRONG.

"When the vents in your plumbing drain system are clogged, the flow of water can slow down or stop altogether. The vents admit air to replace the vacuum of rushing water, and when they are completely blocked, the effect is much the same as covering the end of a full drinking straw with your finger. The water stays where it is."

If you still want to dispute it, quit spreading misinformation and simply ask a professional plumber or take the time to read and educate yourself.

Required venting is very dependent on the system design. Overall, venting is to prevent traps from being sucked dry and allow for the escape of sewer gas. If the top of the vent is caped, a smaller drain will slow down until air can be sucked through the drain.
 
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