Complete newbie to DIY-ing as well as Plumbing.

My wife and I decided to upgrade our kitchen sink and we chose a single basin, 9" deep model. I've been reading a lot on plumbing best practices and racking my brain at how best to move my garbage disposal to the right ( given that the new sink has it's drain on the R.H.S )

the following are a few of the obstacles that I can't figure out how to deal with ( see images )


  1. There is little clearance from either one of the drain pipes coming from the wall as well as being glued to a wye and a tee? ( respectively ) So I don't know if cutting the fittings is advisable.

  2. The vent is very high at this point and will definitely be an obstacle for the newer deeper sink So I don't even know how to deal with it, should I cut and recap? can I cut and recap? If I cut won't the lower diameter portion of the existing fitting be stuck in there?

  3. What could I do with the p-trap coming from the lower drain's wye which I intend to connect to the disposal ( which again, I want to move to the RHS ) given that I think the trap would have to sit low-ish and the RHS drain is high.

  4. Where can I install the new vent IFF I can somehow figure out what to do about the other one, my Idea is to use the capped branch on the lower wye.

I apologize If I used terms incorrectly, again, I'm a newbie ( for what it's worth I'm incredibly excited about this project and have nothing but the utmost respect for the professionals who do this challenging job every day )

I have attached a couple of pictures in hopes of making this a bit clearer.

I'd appreciate any input.

Ps: while I appreciate any kind of input, please do not suggest "leave it to a professional" as my goal is learning, personal growth, and a nicer sink than what I have right now... let's be constructive if we can.

figure 1, question 1

figure 2, questions 2,3,4

  • 2
    Here's one of the joys of plumbing: All of those P-Traps simply screw together and are fully adjustable. You can start by removing everything that unscrews, pulling the old sink out, dropping the new sink in, then fiddling with all the fittings to see what will fit and what won't. If you're totally stumped, you can put the old sink back in and screw everything back together so you have a kitchen sink while you think about it for a few days! (That's also a good time to take more pics and ask how to fix the exact thing that isn't working right.)
    – FreeMan
    Oct 29, 2020 at 12:37
  • Do your neighbors' installations have dual drains? It is hard to imagine why such might exist. Maybe you are in a region that has peculiar requirements? What is your rough location? U.S.? U.K.? Is there a roof vent?
    – wallyk
    Oct 29, 2020 at 16:05
  • 1
    @FreeMan that sounds like a very reasonable approach, I will follow your advice and test/dry-fit, thanks for the insight on the p-traps.
    – lcb
    Oct 30, 2020 at 5:59
  • 1
    @supercat you know, you bring up an excellent point, I hadn't thought of that, also, I forgot wallyk I will ask my neighbor about how his setup looks, he's been at my community for a while he probably knows.
    – lcb
    Oct 30, 2020 at 6:02
  • 1
    If you get stumped, take some more of your excellent photos and post a new question here. Right now, we're dealing with theoreticals and "what-ifs", which is why it's hard to come up with a good answer for you. I think your best bet is to try it and see what happens. Expect that it will take a couple of days and several trips to the hardware store to get different parts. Plan for not needing the sink for that long, and be ecstatic if you manage to finish sooner.
    – FreeMan
    Oct 30, 2020 at 11:11

2 Answers 2


Good pictures. You have an unusual configuration for that drain. Typically, there is only one drain line coming from the wall into the kitchen cabinet. That would have one trap and upstream of the trap are the sink, disposal, and perhaps a dishwasher drain (you don't appear to have one in this cabinet.)

What you have is not necessarily wrong, but if you search for garbage disposal drain on Google Images you will see many examples of more typical configurations. Yours could be like that if you re-orient the disposal and re-configure the drains to combine into one trap.

If it's easiest for you, you could use only the lower drain, and stop using the upper connection. It seems like you need room for a deeper sink and that may help.

Why is your sink drain unusual?

The gotcha question is -- why is your drain setup unusual? And why is that Air Admittance Valve (AAV) (not exactly a vent but it has a specific purpose) connected to the upper drain? Does this drain lack a proper vent at all? Check outside your house and see if there is a roof penetration for the vent above your sink or elsewhere in your kitchen area. If not, that AAV -- which is not a total substitute for a vent -- will need to stay in there somewhere downstream of the trap -- but you could cut some drywall away and see if there's room to relocate it into the wall cavity (just don't cover it with new drywall after; you cannot cover up an AAV because they have a limited lifespan and need to be serviceable.)

FYI the Black & Decker The Complete Guide to Plumbing book is great, well illustrated, and you can find it at many libraries. I recommend you read it or another plumbing book so you can have a better understanding of traps & venting. That may help you understand your options for making changes to this drain better.

  • 6
    I agree - figuring out why it was plumbed this was is critical to ensuring the new work is done properly.
    – FreeMan
    Oct 29, 2020 at 12:32
  • 5
    Rule #1 about finding something weird; you need to know why it is weird before declaring it is "wrong", because you might be wrong.
    – Nelson
    Oct 29, 2020 at 15:53

There are only a few things here that are truly important.

  1. Will the depth of the sink interfere with the AAV? If it does it probably makes sense to remove the AAV and cap the top drain. You only need one of the drains. When capping it leave as much stub as you can for possible future use.
  2. If you use the bottom drain it needs to be vented. If there is no roof vent or other vent present, using a tee you can add an AAV between the garbage disposal and the wall drain. Attach the tee to the wall stub using PVC cement. The other end should have a pressure fitting for the tailpipe from the P trap.
  3. You need to make sure that the P trap is set up properly with a proper weir and proper slope from the crown weir to the drain. See illustration.

Don't stress over how to fit the PVC drain pipe connecting to the lower wall drain. Drain pipe comes in many configurations, it has slip fittings and is easily trimmed if necessary. It is very forgiving - just check for leaks when you're done. Once you have the sink installed with the disposal, installing the PVC drain pipe will be the easiest part.

If the sink doesn't interfere with the AAV you can use either drain and cap the other.
enter image description here

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