Yet another single to double vanity question

Hi all,

What a great resource! I would appreciate any advice you could offer.

I've been searching on this forum but couldn't find my exact situation so bear with me. We would like to take out our single vanity and replace it with side-by-side pedestals. Thus, the traps will be visible and can't be hidden under a sink. I have posted a diagram that shows my current setup. I don't know how to change the drain for the two pedestals though I stuck an idea in the diagram. Would this work or do you have other suggestions? The drain pipe/vent pipe part is at the far end of a wall and goes down into concrete, I think, so it won't be easy to move.

Thanks for any help you can offer. Sorry for the awful diagram. I can try to provide more detail.

It looks legit. The right pitch must be maintained and the proper fittings used.

Thanks for the input. Would you mind elaborating on the proper fittings and pitch? I think I know what you mean but I want to make sure to do it right.

Use Wye's not Tee's to connect the waste arms along the "horizontal" part. The slope is 1/4" per foot.

david

Please see my more detailed drawing. I included wyes where I think they would make sense, where water will flow. But for the extra bit of vent I drew in tees since no water goes there. Do those need to be wyes as well?

Doesn't look right to me.

You would be better off putting a santee below the other santee, running toward the second lav, come up with a LT 90 el, and put the trap arm santee on the verical, and then revent back to the main vent stack.

If you were to come up between the two lavs, you would use this fitting.

drop one more vent vertically down to connect into the segment of pipe that is between the stack and the closest P trap; segment is currently drawn as a straight pipe. Repost and see if plumbers agree that this is sufficient venting. Each P trap will have one vent downstream of it before any other P trap. One vent per P trap. The purpose is to prevent a possible sucking dry of ant one P trap when a full head of water flows past on its way to the stack.

david

Terry and David, thanks for the replies. I'm not sure I understand what you are saying exactly but here's a new drawing...tell me if I got it right. I think I get what you're saying...without the extra venting after Lav2, water coming from Lav1 could suck water out of Lav2's trap. The venting I first drew would keep water leaving Lav2 from pulling water out of Lav1's trap. So this should prevent both things from happening?

Let me know if I'm way off, here, and if the fittings I'm using will be okay.

Thanks!

There's nothing wrong with the second drawing you show. There's no reason to have that second vent. Just make sure the height of the vent line is above the flood level rim of the pedestals before you go horizontal with it. Have fun!!

that is reventing

i think when Terry said to revent, he meant the same thing as how I described it and how you have now drawn it. Where you drew it, it looks a bit low but that is not a problem; the minmum is at least 6" above the highest point (i.e. flood rim) of your sink.

i think Terry said to run two separate drain "arms" out from the stack, but i think that is not the only way to do this, and the way shown now with two vents for two P traps is OK, AFAIK.

also, you can connect the second vent directly into the first vent pipe drawn above it, instead of drawing it off the main vent, in case that happens to be easier to do in reality.

it seems some people think that this second vent is a bit too much.

david

How about this?

Okay, so we don't like that the horizontal vent runs are not higher up in the air? The lower of the two (venting Lav2) needs to be at least six inches above the overflow in the sink? I assume this would not be an issue if I just ran the pipe straight up into Lav1's horizontal pipe as David suggests? That would actually be easier if it's appropriate.

Thanks for the advice.

I'm still a little puzzled about the need for the second vent since there is disagreement. Better safe than sorry, I guess?

Amendment: Thanks, Frenchie, for the drawing...you posted as I was posting!

right. The drawing didn't show scale, so someone commented that the new vent had to be high enough. No big deal.

Someone else said it was now more than enough venting. Subjective use of the word "more", true enough, but better safe than sorry, and better fully compliant with code than not. It's like tax law; there is only one clause on each subject in law not several but still there are times when differing views collide and readings end up with different results. Still, no-one will deny that each trap needs a vent. I am not an expert.

david

Is this the scheme Terry wanted? Should I still have a vertical pipe after Lav2 connecting to the revent?

I had to dig around to learn some terms. Also, what I now have labeled as a santee in the stack I had drawn as what I thought was a wye. Does this need to be a wye or is a santee correct?

This is crazy!

What Terry said in few words was almost that, I think. Not to worry. I had a hard time understanding it too. I think it's this he meant: take yesterday's drawing and change only one thing: each P trap gets one vent and one san-tee connection to the stack, instead of running both through the same drain connection to the stack. Or, take this new diagram and drop a vent down to the unvented arm. "Revent" is when you tie two vents together, and that is what you are missing here now in this latest diagram. Later, he might say that is overkill. I think the way it was drawn yesterday is perfectly adequate, and in many cases is the only physically possible installation. I'm not a plumber.

You might ask, "why does a single P trap on a short distance arm require a vent now, when it never had one before?" The answer has to do with this elusive subject called wet venting, and I know for sure that I am not the right person to explain it and describe it perfectly, so I'll leave that for a Master Plumber.

it seems vents now go on waste arms no matter how short, for optimum security. I never saw any discussion of this in terms of the code having changed to now require it, so I'm curious about this too.

When you have two P traps on an arm, a single vent is not enough to ensure safety and security (sewer gases, P trap emptying, etc).



david

trap

As Henry Higgins said, "By Jove, I think he's got it." That final drawing is the way to do it. You do not have one sink flowing past the other one, and if you did it the original way, you would not be able to "hide" the combination Y-1/8 bend fittings in the wall. They would be too wide.

Don't you just love learning new stuff??

Funny you mention that about that original one-sink design without the vent on the horizontal arm. I was just wondering on the way to work why it didn't have it in the first place. That sink has never drained well and I bet that's why!

Okay, add the vertical pipe from Lav2 to the upper pipe. Got it.

OH! What size pipes do I need for all this??

vents

You are misdiagnosing the problem. The original riser pipe was the vent, and the side arm did not need a duplication of it. The previous poster was incorrect when he said, ALL arms need vents regardless of their lengths. Whether a drain needs an additional vent or not depends on a lot of factors, but if the arm is short, i.e., under 4' there would have to be other considerations before adding a vent. In addition, vents do not make a sink drain better. If there are no other problems, namely problems that having a vent is concealing, a sink will drain better without a vent.

Thanks, HJ. After I posted that I googled "wet vent" and didn't find very much but I did find that my old setup is a wet vent and it wasn't wrong. Interesting stuff.

Please bear with me as I'm really trying to learn. I find this pretty fascinating.

Why would the additional lav need the top venting if its waste is run as a separate line? I ran across a diagram that showed several waste arms running into the same stack, all with the configuration of my original vent. The point was since they were all wet vents, they were okay. Perhaps the diagram was wrong? I'm not pretending to understand the wet vent concept, just that it seems my "Terry" diagram without the top leg seemed to be the same as this diagram had. Hmm...wondering if the LT ell has something to do with it....

Just curious...I'll do it the way y'all tell me!

How close is close enough?

I have finally started work on this. I have a probably minor concern and I couldn't find anything similar on a quick search, but maybe I just wasn't looking for the right keywords.

Anyway, the sink instructions say to have the waste pipe 20" above the finished floor. I'm not sure I can do it with the configuration in the last diagram I made. It will end up being 21" or maybe 21 1/2". Is this going to be a problem? I would think there has to be a little "fudge factor" here but wanted opinions from those who should know.

Thanks!