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Understand this is asked often. Each case is different though and have not found someone with my plumbing configuration (see pictures).

So when we turn on garbage disposal we get water shooting up non-disposal side just about every time. I am almost sure it is not a clogging issue. As a test I filled non-disposal side sink entirely with water and pulled plug, observe no water backing into garbage disposal or garbage disposal side sink (i.e. it is going down drain quickly). I am convinced this is one of those "garbage disposal shoots with great velocity, takes path of least resistance, goes up non-disposal drain".

I have attached pictures of my plumbing.

Based on all I have read it seems the disposal drain needs to tie in using a T-Baffle to force the waste to go down and not shoot across the 4 way connector. If you look closely a lot of the pieces are glued. I don't think I can get that 4 way connector out without cutting.

What would be the best solution? Some sort of check value in the non-disposal line?

enter image description here

enter image description here

Update - Added additional sketches and a picture of our home exterior to illustrate it would be difficult to have an exterior vent.

Jay's Solution

Jimmy's Solution. Question - where would AAV go? Jimmy's Solution.  Question - where would AAV go?

Exterior - I have included this picture to illustrate how difficult it would be to have exterior vent. The top of the 2nd roof is rubber/flat. The vent stack for bathrooms is far removed. Exterior - I have included this picture to illustrate how difficult it would be to have exterior vent.  The top of the 2nd roof is rubber/flat.  The vent stack for bathrooms is far removed.

Double Wye - Could I simply replace the 4way connector with this? double Wye

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    What's the thing atop the cross fitting? An AAV? Is there a way to get a conventional vent to this complex? – ThreePhaseEel Mar 10 at 23:41
  • yes. That is an AAV. By conventional you mean vent that would go out roof? – M Schenkel Mar 11 at 0:23
  • Yes, a vent that connects to a roof venting stack – ThreePhaseEel Mar 11 at 0:25
  • would be very difficult. This is a home. – M Schenkel Mar 11 at 0:41
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    You could put the plug in the drain of the sink when you run the disposal. – Willk Mar 11 at 0:54
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Apologies for the mickey mouse sketches. There are lots of CAD gurus here who would rightly shame me for this .... but anyway .... top is what I believe @JimmyFix-it intends. I think it's the better suggestion. Bottom is roughly what I've suggested. Shaded in the top diagram, two baffle tees, and in the bottom, two wyes offset vertically. Yes there's an AAV either way. Try to shove it up between or behind the sinks as shown.

Either way you should add a cleanout, which I forgot to draw. If you use compression drain fittings for the baffle tees you don't need to add one, but if it's all glued up you can add a straight compression fitting between the AAV and the tee it joins.

enter image description here

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  • Looks just like mine. Except I have disposal T/Wye below the non-disposal sink T. In your original response you said to drop the disposal drain. So I figured this meant it would go lower. – M Schenkel Mar 11 at 13:17
  • Two sad souls without CAD skills. :(. Yes you drew my solution correctly, ha ha, the disposal should connect below the sink. Partly because you'll find it easier to stack it that way in the limited vertical space. But you should have added a vent to the other solution, and it has to go after the trap. You could use a wye instead of a tee for the trap/vent connection, if you have space. The benefit of using a tee in Jimmy's solution is that the disposal enters it vertically. – jay613 Mar 11 at 13:21
  • Also with the single-trap solution from Jimmy Fix It you can rotate the disposal around so you don't need so much pipework. You may even be able to put the disposal elbow DIRECTLY into the top of the first tee. – jay613 Mar 11 at 13:27
  • Thanks - you have been most helpful. So both could work. So with your solution if I have limited "vertical space" to work with I could make use of the double wye? – M Schenkel Mar 11 at 13:28
  • One more thought. If you have an unfinished basement beneath this there is a way to vent this through the floor without an autovent. I don't have a preference but some people prefer to not have a mechanical device. As long as you are ripping it all up, have a look. Look up "island sink venting" for diagrams. – jay613 Mar 11 at 14:00
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Replace that 4 way junction with two wyes offset from each other (you might drop the disposal trap a few inches to achieve this) and extend the aav arm as high as possible.

The pressure from the disposal may be forcing the aav shut, and between the poor configuration of the hub and the resultant lack of venting the opposite sink is the path of least resistance.

Yes you will have to chop that monster out. If you can't configure two offset wyes at least get a double wye hub and raise the aav.

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  • "If you can't configure two offset wyes at least get a double wye hub and raise the aav." - Is my picture labeled "double wye" what you mean? – M Schenkel Mar 11 at 13:20
  • No. I mean if there is not enough vertical space for one wye above another, use a double wye like this s3.amazonaws.com/s3.supplyhouse.com/images/products/zoom/…. but at this point I hope you'll go for the solution that eliminates one of the traps. – jay613 Mar 11 at 13:25
  • I'm not sure of the timing of the edits and comments, but that double wye you listed, jay, appears to be exactly what @MSchenkel edited into his original question. – FreeMan Mar 11 at 13:30
  • @FreeMan correct, it was a timing issue, his comment appeared before his picture, I even refreshed the page a few times and could not see it. – jay613 Mar 11 at 13:34
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Get rid of that double trap setup and that PVC tee monster. Configure a single p-trap to a waste ell on the vertical waste pipe coming out of the floor. A baffle tee goes to the top of the trap with the garbage disposer dumping into the top of it and the other sink plumbed into the side port of the baffle tee. Do not use any of that flexible accordion type fles anywhere in the system.

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  • Do I need an AAV? Where would that tie in? – M Schenkel Mar 11 at 12:18
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    Tee goes after the trap. If you can make it fit vertically I prefer this to my suggestion. Might be hard. The top of the baffle T has to be below the elbow out of the disposal. The trap beneath the tee. Then the exit from the trap should join the angled part of a wye that will go up to the air valve and down to the waste. – jay613 Mar 11 at 12:38
  • @jay613 - my comment/question regarding the AAV was specific to jimmy-fix-it solution. I think I understand what you are saying. I will post a sketch. – M Schenkel Mar 11 at 13:08
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Et voila. This is what you should aim for, but where I drew the red circle you'll replace the wall tube with another tee that goes up to the vent and down to the drain. Turn the disposal around as pictured here. Use drain tube just as pictured here rather than gluing anything then it's easy to align everything and you don't need a cleanout.

enter image description here

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I am not recommending this but only because it reminds me of Terry Gilliam's movie Brazil I'm adding this $28 all-in-one monstrosity solution. You would add an AAV instead of a wall flange.

enter image description here

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  • Thanks - many ways to skin a cat. What is that nipple looking object on the non-disposal drain/elbow? Almost looks like an AAV of sorts. – M Schenkel Mar 11 at 14:25
  • The nipply thing is for the dishwasher, and the disposal's dishwasher inlet is pictured unplugged because, um, IDK though my last disposal came with that inlet sealed as part of the molded casing that had to be drilled out. – jay613 Mar 11 at 15:10
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    You mentioned you aren't recommending this. Can you add to your answer why you are not? – RockPaperLz- Mask it or Casket Mar 11 at 16:43
  • @RockPaperLz-MaskitorCasket The purpose of the answer was to provide some amusement to those whose life experience includes both this Question and that movie, rather than a recommendation for or against flexible pipes. I know there are strong feelings on the topic. I don't think I'l overburden my answer by including this explanation in it. To my horror, someone has upvoted it. – jay613 Mar 11 at 16:55
  • To my horror, someone has upvoted it. LOL! Now two people have upvoted it. I plead temporary insanity. – RockPaperLz- Mask it or Casket Mar 11 at 16:58
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Use disposal inlet and drain sink into disposal.

I lived in a house where the sink drained into the disposal. It looks like you drain the dishwasher into the disposal already because that port is in use by some flexible pipe. That intake could do double duty. You would need some sort of T adaptor.

In the house where I was the sink would back up if the disposal needed to be run, just as the disposal side does if the disposal needs to be run. There is an easy fix for that: run it.

You could keep the much here-hated on T outlet you have now (which has the benefit of already being there) and just cap the sink side. Then use the also hated on flexible stuff to make a drain line similar to that used for the dishwasher.

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