I was told that I needed a 3" drain pipe to self vent the sink. I have searched all over to see how to plumb 1 1/2" drain pipe into a 3" pipe with no luck. a picture is worth a thousand words. Working with Arkansas code...tnx

You'll use a 3" x 3" x 1-1/2" PVC DWV Sanitary Tee. It's important that you use a sanitary tee, and that you fit it in the proper orientation.

3-x-3-x-1-1-2-PVC-DWV-Sanitary-Tee

Or a 3" x 1-1/2" PVC DWV Reducer Coupling

3 x 1-1/2 PVC DWV Reducer Coupling


Venting island fixtures can be difficult, since you obviously can't simply install a vertical vent pipe. The Family Handyman has a good article on How to Plumb an Island Sink

You'll notice the article provides two methods, either you provide a separate vent line, or you use an air admittance device (AAV). The AAV method is only going to be accepted in some areas, so check with your building department before going that route.


As for which way to install a tee. If you're installing a straight tee, there's no wrong way. If you're installing a sanitary tee, you'll have to pay attention to the direction of water flow.

Let's say you have a sanitary tee like this

Sanitary Tee

If the flow is down like this...

Sanitary Tee Water Flow

You can have water flow in like this...

Sanitary Tee Proper Water Flow

If you have the tee like this...

Sanitary Tee Upside Down

It's upside down, and you can't have water flow in like this...

Sanitary Tee Improper Water FLow

  • Tnx, I have both of these fittings, but I would still like to see how to put them together so the inspector won't reject the work...he doesn't like the fact I'm not a plumber and is sure to comment on the job. – Dave Mar 20 '15 at 14:28
  • So the question is "How do I join PVC fittings?", is that correct? Do you have PVC primer and glue? – Tester101 Mar 20 '15 at 16:22
  • Or is your question even more broad, and should be "How do I plumb a drain from an island kitchen sink, and tie into a 3" drain?"? – Tester101 Mar 20 '15 at 16:30
  • Please...I know how to glue materials together. You know that T fittings can be glued inverted, right. I didn't until an inspector trashed a lot of my work (mostly vent lines) saying I had inverted T" – Dave Mar 20 '15 at 17:20
  • ...with the p-trap directly above it? Or would he want to see the 3" tee keep going vertical with a cap and the p-trap entering from the side of it? – Dave Mar 20 '15 at 17:30

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