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stan 41943 02-29-2008 08:52 AM

Vent stack for kitchen sink
As a newbie I would like to commend this site & especially its regulars -so many problems solved! I am completely redoing my kitchen after 13 years. The island kitchen sink with disposall and dishwasher has no vent yet it has functioned perfectly. There is no way for me to install a through the roof vent but I could copy the design of my utility sink in the basement with an 8ft vent in a wall 4ft from the drain line. Is this worth doing and how small diameter does this vent need to be?

Double A 02-29-2008 11:07 AM

Island sinks can be vented in more than one way. Not seeing a pipe coming out of the counter top and rising to disappear into the ceiling doesn't mean its not vented.

If could be on a continuous wasted and vent system, whereby the branch drain for the island is oversized intentionally to allow air to vent above the water level, or it could be loop vented.

You say this setup has worked well for several years, so, what makes you want to change/correct it now? Has something changed?

stan 41943 02-29-2008 03:22 PM

No nothing has changed- as a matter of fact, when the house was built the plumbing rough in looked like a work of art. Now after your explanation I'm once again impressed with their job. Won't change a thing. Thanks! That said, would be interested to learn about Loop vent & continuous wasted & vent systems. Guess they are commonly used in islands.

Double A 03-02-2008 06:00 PM

Example of a loop vent

Swiped from :

stan 41943 03-02-2008 07:10 PM

Thanks. Great article in readers digest. Took a picture of my system but the site rejected because too many bytes.:censored: There is no trap above floor but there is a cleanout & the lines are BIG - 6"circumference -2"? Don't know how to send drawing.

Double A 03-06-2008 12:11 AM

You really do need a trap. For safety and health reasons your sinks should be trapped.

If you upload your picture via imageshack, you can link it here by using the "insert image" and pasting in the direct link to it. I think there is a current discussion on that in the help and site suggestions.

I have not found a good image of a combination waste and vent, but be advised, its not code approved everywhere.

Other than the trap, it still sounds like you're in good shape.

stan 41943 03-08-2008 03:21 PM

1 Attachment(s)
Finally figured out how to send a picture. I believe there is a trap under the island.

Double A 03-10-2008 12:41 PM

Hmm... that doesn't seem like it would meet code based on any of the model codes I'm familiar with. The disposer should be separately trapped from the other bowl of the sink, that is assuming it is trapped under the island.

That is the other problem. That trap in addition to being two traps, should be accessible and of a type that will allow it to be taken apart and cleaned.

It seems that you have no vent, or a combination waste and vent system. Without seeing the rest of the plumbing, its hard to say for sure.

stan 41943 03-12-2008 04:16 PM

Double A, thanks so much for staying with me on this (I've also had computer problems this week). I realize that you are reluctant to endorse anything that doesn't meet code and that code varies in different locations.Just a theoretical : in the non code system pictured which has worked quite well for 12+ years, would putting traps on one or both sink drains be advisable, or is it more likely that no changes would continue to function best?:whistling2:

Double A 03-13-2008 01:10 AM

Before you make any changes, look for a trap under the island.

If there is one there (and I can't for the life of me imagine a real plumber ever doing that) then adding more traps may be asking for trouble if you don't remove that hidden trap.

In a more perfect installation, you'd have your sink bowl and the disposer trapped individually and no trap under the floor.

Take a look and let us know.

p.s. Worst case (no trap under the floor) is you're allowing gases from the sewer system back into the house which is quite unhealthy. Best case is you have some screwy plumbing that is functioning (meaning, its trapped under the floor).

justdon 03-13-2008 06:34 AM

exactly same problem as my daughters.
I was at my daughters NEW home,,in the last year or so,,,and she was standing over the sink an said they were having a problem,,,the disposal on one bowl of her sink threw dirty water into the OTHER bowl,,,sometimes.

I look under the sink and the dishwasher drains into top of disposal,disposal discharges into a 'straight' pipe over to the tee where the other bowl drains, then goes DOWN into the trap and then exits thru the wall.

So disposal MUST be throwing crap against far wall of that tee and UP into the bowl. Is this a code infraction to NOT have a disposal trapped on its own?? I never messd with disposals before cause septic tanks dont like them,,,is it 'standard practice' to trap each side?? Can they add a trap the disposal stuff twice,,,meaning adding a trap to the horizontal pipe to the tee,,,and it draining into the existing trap??

Bigger question,,,after a year or so,,is this something the builder(cookie cutter tract housing) 'SHOULD' come back and redo?? thanks--those pics were def. interesting,,,to see how others solve these issues!!

Double A 03-13-2008 11:37 AM

First of all, understand this. Codes are written to ensure safety and functionality first and foremost. Sometimes the code makes sense to anyone that reads it, sometimes it makes little sense and seems inconvenient. That is when we get situations like your's and your daughters plumbing issues.

Most model codes call for a separate trap for a disposer for just this reason. The disposer can push dirty water into the other bowl of the sink where there might be clean food or dishes and contaminate them.

Its not a likely situation, but codes look more at possibilities, not really probabilities. Some local code officials think this such a low probability that they give in to pressure to exempt or cut out this section of the code for single family dwellings, but may still require it for churches, schools, day cares, etc.

The setup you're seeing in your daughter's home is called a continuous end-outlet waste. Its designed for two sink bowls to share a trap. I don't know what your local code calls for, but after one year, I wouldn't think the builder/plumber would have any responsibility to make corrections now.

Continuous end-outlet waste

Take a picture and start a new thread. We can tell you how to add a second trap to the disposer if you want to tackle it. If not, its usually not a lot of bother for a good plumber to change it over.

Or you can check out Kirby Palm's page on a disposer installation he did. Really good drawings and a nice picture of a disposer on its own trap. He's made the sink drain on one bowl a bit more complicated than need be, but nice work for a DIYer. His installation didn't include a dishwasher drain.

Ron The Plumber 03-13-2008 03:21 PM

Double trapping under kitchen sinks are not allowed where I'm at, against code here.

UPC Code

Double A 03-13-2008 04:57 PM


Originally Posted by Ron The Plumber (Post 107355)
Double trapping under kitchen sinks are not allowed where I'm at, against code here.

UPC Code

Ron, you're referring a trap, followed by a trap, not one trap on the left kitchen sink bowl, and one trap on the disposer connected to the right kitchen sink bowl, and both tied into a wye and then out the back of the cabinet, correct?

I'm just trying to get our terms straight.

Double trapping in my experience is one trap followed by another trap and is not allowed under most model codes, unless the second downstream trap is a house trap.

Ron The Plumber 03-13-2008 05:25 PM

Yes only one trap allowed under KS, you can't have two traps, i.e. two traps connected to a wye one to the disposal and other to opposite side of the sink.

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