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Discussion Starter #1
Hi all,

I'm noticing the kitchen island sink drains relatively slow compared to the main sink. For example, if I'm washing 2-3 dished in the main sink, the water at full pressure goes down the drain quickly enough that there is no build-up of water in the sink.

On the island sink however, with the water at full pressure there seems to be a few millimeters of water building up in the sink. Once I shut the faucet off the water goes down noticeably slow and sometimes (just a handful of times) bubbles.

I've noticed though, when I fill the sink up 1/4 way or more with water (to soak veggies etc), then release the sink drain, the water drains incredibly fast. New the end, it makes a faily loud "wooooshing" noise as the last bit of water goes down.

What gives? The house was renovated last year and I never really used the island sink. I know it's vented, but the vent is roughly 7 ft away from the sink. Would adding a cheater valve help at all, or am I dealing with something else here?
 

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Partial blockage somewhere vent, line or both. Try plunging the island sink. If still no good, remove trap, clean it, and snake from there.

No biggy, kitchen sinks are notorious for clogs. Do same for main sink as well. See if that helps.
 

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Naildriver
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Depending on how far your island is from the venting, it may require a Studor vent (Air Admittance Valve).
 

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Discussion Starter #5 (Edited)
Thanks for the replies.

The island is net-new, meaning there was never an island there before. The contractors had to add all new plumbing for the drain. I don't think there would be any blockage as it was hardly ever used since new.

I recall measuring the the island sink drain to be about 7 feet away from the vent connection/stack (not sure what it's called). I'll try adding an Air Admittance valve to see if it helps.

I'm still curious though...why would it drain fast when the sink is filled, but drain kind of slow when using it normally (or having it slightly filled)??

I'll try to get a video of it.

EDIT
Here it is draining slow with about 1/8" of water in the sink


Here it is draining with about 4 inches of water
 

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I agree, It does appear it's starving for air by the sounds it's making at the end. But imo, no biggy. It works and it's not sucking any traps dry. As mentioned, probably a studor or aav vent would help.

For any drain to work properly, you need air behind the water. This is why we vent the dwv.

For example, the old straw in a class trick that we all know, where you insert the straw into a glass of water, hold your thumb over the end of the straw, lift it out of the glass and water stays in it, then release your thumb and the water comes out.
 

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Under IPC you can use combination drain and vent method on the island sink. The pipe must be 2 inch and no garbage disposals installed. Vent location doesn't matter.
I would look and make sure your plumber has pitch on the pipe 1/4" per foot. But overall I don't see an issue.
 

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Naildriver
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I know most islands here will have an AAV, since basically you will be installing an "S" trap to tie it into the downline plumbing.
 

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Naildriver
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What distance limit would you require a vent. OP says his is over 7' away. If you are a plumbing inspector, then bless your heart.
 

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What distance limit would you require a vent. OP says his is over 7' away. If you are a plumbing inspector, then bless your heart.
Under Combination drain and vent the pipe would need to be 2 inch in size the vent could be anywhere on the same horizontal plane. Your from an IPC state I’m also a 28 year plumber before becoming an inspector. I would think you would know this venting method. It's in chapter 9 of your code book.

SECTION 915
COMBINATION WASTE AND VENT SYSTEM

915.1 Type of fixtures. A combination waste and vent system shall not serve fixtures other than floor drains, sinks, lavatories and drinking fountains. Combination waste and vent systems shall not receive the discharge from a food waste disposer or clinical sink.
915.2 Installation. The only vertical pipe of a combination waste and vent system shall be the connection between the fixture drain of a sink, lavatory or drinking fountain, and the horizontal combination waste and vent pipe. The vertical distance shall not exceed 8 feet (2438 mm).
915.2.1 Slope. The slope of a horizontal combination waste and vent pipe shall not exceed one-half unit vertical in 12 units horizontal (4-percent slope) and shall not be less than that indicated in Table 704.1.
915.2.2 Size and length. The size of a combination waste and vent pipe shall be not less than that indicated in Table 915.2.2. The horizontal length of a combination waste and vent system shall be unlimited.
TABLE 915.2.2
SIZE OF COMBINATION WASTE AND VENT PIPE


MAXIMUM NUMBER OF DRAINAGE FIXTURE UNITS (dfu)
DIAMETER PIPE (inches)Connecting to a horizontal branch or stackConnecting to a building drain or building subdrain
234
626
31231
42050
5160250
6360575

915.2.3 Connection. The combination waste and vent system shall be provided with a dry vent connected at any point within the system or the system shall connect to a horizontal drain that serves vented fixtures located on the same floor. Combination waste and vent systems connecting to building drains receiving only the discharge from one or more stacks shall be provided with a dry vent. The vent connection to the combination waste and vent pipe shall extend vertically to a point not less than 6 inches (152 mm) above the flood level rim of the highest fixture being vented before offsetting horizontally.
915.2.4 Vent size. The vent shall be sized for the total drainage fixture unit load in accordance with Section 906.2.
915.2.5 Fixture branch or drain. The fixture branch or fixture drain shall connect to the combination waste and vent within a distance specified in Table 909.1. The combination waste and vent pipe shall be considered the vent for the fixture.

Sorry about how it pasted.

639206


639207


Hope this will help you.
 

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Naildriver
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I am a naildriver, not a plumber, so I am learning theories here. We don't know the size of the venting the OP has, but he has stated that the vent is over 7' from the island. In the islands I have seen, there is no trap arm, but an "S" trap, which I understand is not code compliant. I don't know how the OP has his set up. I don't see how the water in an S trap can keep from being sucked out unless an AAV is installed. Help with those theories so maybe the OP and others can understand more fully.
 

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I am a naildriver, not a plumber, so I am learning theories here. We don't know the size of the venting the OP has, but he has stated that the vent is over 7' from the island. In the islands I have seen, there is no trap arm, but an "S" trap, which I understand is not code compliant. I don't know how the OP has his set up. I don't see how the water in an S trap can keep from being sucked out unless an AAV is installed. Help with those theories so maybe the OP and others can understand more fully.
 

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639277


S Trap

639278
The one on the right is a ptrap. Under combination drain and vent the piping needs to be 2 inch at the top you install a 2 inch by 1.5 inch 90 and a p trap.

The vent is the oversized pipe . With the flat part off the P trap it kills the syphon you get from an S trap. Remember there has to be a vent somewhere on the same horizontal plane (no jump ups allowed on the drain until it turns vertical you can also have a vented fixture to meet the venting requirements for combination drain and vent)

Hope this helps.
 

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Naildriver
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It helps. But explain how this would work on an island where a vertical trap is not practical as shown in your ptrap drawing. Would just the horizontal piece act as a vent since it is going into a 2" pipe??
 

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A 2 inch pipe is oversized so air travels through the pipe and waste also. The island sink can not have a garbage disposal but every thing else is approved for use 1.5 inch is the normal size pipe for a sink if it has a vent as shown.

I'm not understanding your vertical trap? Also, a S trap is 100% illegal to use under IPC.
 

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Naildriver
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OK, I know S traps are illegal. How do you drain an island, since it has to go through the floor? Do you use a horizontal piece of pipe as you show without the vent?
 

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@Ghostmaker I understand what you are explaining. However, this is strictly IPC. It would not fly per UPC model code. You would need a AAV or island vent. UPC kitchen sinks are always 2" per sizing chart
 
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@Ghostmaker I understand what you are explaining. However, this is strictly IPC. It would not fly per UPC model code. You would need a AAV or island vent. UPC kitchen sinks are always 2" per sizing chart
Look at my post 7
Under IPC you can use combination drain and vent method on the island sink. The pipe must be 2 inch and no garbage disposals installed. Vent location doesn't matter.
I would look and make sure your plumber has pitch on the pipe 1/4" per foot. But overall I don't see an issue.
 

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Chandler if the pipe is sized per the dfu for the sink and somewhere on that same horizontal plane it has a vent or a vented fixture all you need do is run the oversized pipe into the cabinet and turn up same size and pick up the P trap and sink.

This is why for example if one has a vented bathroom in the basement one does not need to vent the floor drains. But if nothing in the basement has a vent then you must vent your floor drains. Floor drains fall under combination Drain and vent. IPC code only
 
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