What size PVC for kitchen sink?

PM5K · Dec 13, 2011

I have a kitchen sink I'm working on, and all that is currently there is a 1 1/2 vent pipe. The rest either isn't there, or is just a small amount (a couple of feet) of 1 1/2 PVC.

What should I be using here, and once I'm past the vent, and underneath the home, should I be going to something larger as I go towards the main stack?

Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County

Terry · Dec 13, 2011

The trap and trap arm can be 1.5"
After the vent the waste should be 2.0"
Fifty years ago, they were run with 1.5", but since then the codes have used 2.0"

Sponsor · 2022-01-29T12:20:58-0800

PM5K · Dec 13, 2011

Yeah make sense, I'm fairly certain the original was 1.5.

It's sad that I've done as much as I've done and I don't know that because it's probably pretty basic info.

I borrowed a great book (well to me it seemed great) about plumbing codes. If not this exact one then one very similar to THIS.

Any thoughts on something like that? Seems like it would really come in handy.

PM5K · Dec 13, 2011

I guess I should probably keep this in one thread, but the only other questions I have right at this moment is about what fitting to use near the sink, and which near the main "stack".

This photo shows what I currently have based on advice here, I hope I followed it properly. I haven't had any issues with it, I just need to add the drain for the sink to it. Right now the line from the left is one bathroom, and the line from the top is another. The line all the way to the left that isn't connected is more or less where the sink drain will be coming from. Should I use like a double wye with a reducer? Maybe a separate single wye further up stream from the one shown?

MTcummins · Dec 13, 2011

I'd just use a 3x2 Wye above the existing one.

Make sure you use a SanTee for the connection under the sink between the trap arm and the vent... a wye is not acceptable there. You can get wierd custom SanTees, but I generally just use a 2" SanTee with two 2x1.5" bushings.

PM5K · Dec 13, 2011

For what it's worth, it would probably be easier to use a double wye because the location of the pipe is about where it would be and I'd basically have a straight shot into a double wye. I guess if I used a separate 3x2 I'd waste less pieces of PVC, because with a double wye I'll have to cut out and replace the existing wye, etc.

Is it an okay option to choose either, or is there a good reason not to use a double wye here?

Yeah I think I already learned that one about santees and wyes before.

The question I had about the fitting near the sink was this: After the santee, which fitting would I use to go horizontal?

It's basically going to be the santee, with the vent going up and the drain going down, it then needs to go horizontal a good thirty feet (I know about the 1/4 per foot and I'll also need some kind of straps to support the pipe), and eventually connects to the junction shown in the photo above.

So which fitting should I use below the santee to go horizontally?

Thanks.

MTcummins · Dec 13, 2011

Either 2 45s or a LONG sweep 90 are acceptable. There is a short 90 (called a vent 90, only acceptable in venting systems), a medium 90 (that can go from horizontal to vertical, but not the other way around), and a long sweep 90, that can generally be used anywhere.

You need to strap that pipe every 4' along the horizontal. Your existing pipe is in violation of that as well, while you're at it, might as well do some strapping there. I usually use the grey plastic strap with lots of holes in it, you just cut it to the length you need and screw it to the joists above, down under the pipe, and back up to the joists. The nail on "J" brackets are nice if the pipe is close enough to the floor to use them.

MTcummins · Dec 13, 2011

Oh, and I think the double wye is ok in that situation, but i'm not a plumbing pro... hopefully one of the more experienced plumbers will confirm this.

MTcummins · Dec 13, 2011

Apparently I keep thinking of things after posting today...

Anyway, you should read through this document, gives a pretty good summary of code use of fittings, proper attachments, etc.
Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County

One more thing, especially with that long horizontal run (and I'm pretty sure its code required). You should have a cleanout under the sink, below the Santee, accessible from the cabinet. Alternatively, or possibly do both, you could put one in under the house where the pipe turns horizontal, but I personally don't like doing it that way if there is a better alternative (such as under the sink).

Kreemoweet · Dec 13, 2011

What about your cleanout? The plumbing code I work under requires a cleanout at the upstream end of every
horizontal drain longer than 2 feet (with some exceptions). If you dropped your sink drain into a 2" combo fitting
and glued a cleanout fitting in the upstream hub, you'd be good to go. Cleanouts are especially important on
kitchen sink drains.

PM5K · Dec 13, 2011

I'm not sure, with the current setup, or any reasonable setups, that any kind of cleanout would work inside the home. I also had no idea it was necessary.

I was thinking I'd use a 2 inch 45 degree combo wye with the cleanout on one end and the horizontal run on the other. I'm fairly certain that's what I did with the water closet I worked on in the past.

For whatever it's worth, there would be no problems with accessibility with that setup.

EDIT: Might have to read it again but I think that's what kreemoweet just posted as well.

PM5K · Dec 13, 2011

I figured I'd just post a picture in case I used the wrong fitting name, but this is what I was thinking except with 2 inch pipe instead of three:

MTcummins · Dec 13, 2011

That would work fine. It is the other acceptable way to do it. I just prefer under sink for ease of access, but as long as you have I think 18" behind the cleanout for access, then you can have it in the crawl space. Its just a PITA when you need it.

Why can't you do one under the sink?

PM5K · Dec 13, 2011

I guess I never even thought about it so I can't say for sure. I've seen it done above the santee and that definitely wouldn't work based on the layout. As for underneath, this is on an outside wall on a home that sits above ground, and it has a good seven feet behind the cleanout. It really couldn't be any easier to access.

MTcummins · Dec 13, 2011

In that case, you're probably better off having it down there anyway. If you were to get a clog in the vertical pipe, you can always remove the trap and snake that part through the santee.

I usually put mine a few inches below the santee... above is usually too hard to get to to snake on a kitchen sink, just too much stuff up there. Almost positive both are acceptable, I think the cleanout just has to be before the horizontal run, so the way you're doing it is basically the last place you can put it going downstream. I could be wrong on that though... someone please correct me if I am.

Jimbo · Dec 13, 2011

Just to be clear.....a wye, or double wye, can be used on the horizontal, but NOT on a vertical stack. On vertical, the waste arms must enter through a sanitary tee, or sanitary cross. For back to back fixtures, it is a little different piece called a figure 5.

PM5K · Dec 13, 2011

Are you saying that just to clarify or did I or someone else say something wrong?

MTcummins · Dec 13, 2011

jimbo said:
Just to be clear.....a wye, or double wye, can be used on the horizontal, but NOT on a vertical stack. On vertical, the waste arms must enter through a sanitary tee, or sanitary cross. For back to back fixtures, it is a little different piece called a figure 5.

Correct me if I'm wrong, but isn't this true only of trap arms entering a vertical? I'm fairly certain that you can (and should) use a Wye after the vent to tie together say 2 vertical drains, or a horizontal to a vertical, if the horizontal drain wye is after the vent. I'm not sure if a double wye fits this same rule or not in the vertical.

Figure 5? Can you post an image of this? I thought you used a Fixture fitting for this application? Is that another name for the same piece?

My county doesn't allow basically any of that (I think we can use a fixture fitting for back to back toilets entering the stack, but nothing else). We have to have a separate drain, trap, and vent for each sink, even for each bowl in a kitchen double sink. But we're a little crazy on the extra plumbing rules here, not many places seem to have restrictions like that.

MTcummins · Dec 13, 2011

PM5K said:
Are you saying that just to clarify or did I or someone else say something wrong?

He's just being clear, it doesn't effect the setup you're proposing.

PM5K · Dec 19, 2011

So it looks like the trap arm is actually going to be longer than 42 inches. The book I have says if I use 2 inch pipe for the trap arm I can go 60 inches, is there any reason not to want to use 2 inch pipe for a trap arm vs 1 1/2 inch pipe?

I'm going to have to look at my book, but will a 2 inch trap arm be okay with a 1 1/2 inch vent?

What size PVC for kitchen sink?

Users who are viewing this thread

Member

The Plumbing Wizard

Paid Advertisement

Member

Member

In the Trades

Member

In the Trades

In the Trades

In the Trades

In the Trades

Member

Member

In the Trades

Member

In the Trades

Plumber

Member

In the Trades

In the Trades

Member

Similar threads