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Thread: Where does the P-trap go?

  1. #1
    DIY Junior Member blackm3sedan's Avatar
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    Default Where does the P-trap go?

    It may seem like a simple question, but how do I put a p-trap in here without making it into an s-trap?


    It's a room addition which required a new slab and footing to be poured. I think the rough-in drain line should have been installed in the wall cavity and not in front of it. In this picture, the sink is on the left, which will have the vent, with the toilet in the middle and the problem bathtub drain on the right.


    Any suggestions?

  2. #2
    Plumber jimbo's Avatar
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    You will need to do some digging. You need a tee on the white vertical pipe. The min. distance from the trap to the vertical pipe is about one pipe diameter, so as long as you can fit the tee in and connect the trap waste arm to it, you will meet minimum length almost just by definition.

  3. #3
    In the Trades mtcummins's Avatar
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    so there's no vent on the tub? is this why you're concerned about an S-trap, that you'll be cutting the rough in line down to the trap level with no vent on it? I'm not sure you can do that w/o creating an S-trap. If you can't connect that vent line over into the other vent, you may have to put in an AAV or something, but I'm not sure... hopefully jimbo or someone else with more experience than me will chime back in.

    In looking at it a second time... is there a trap buried in the rough-in? I didn't see that at first... if so, then i think you just need to offset the pvc drain line with a couple 45s and drop the tub drain straight into a 1 1/2" trap adapter, but again, maybe a plumber can verify that this is a legal setup...
    Last edited by mtcummins; 12-06-2011 at 06:30 PM.

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    DIY Senior Member dlarrivee's Avatar
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    You're going to have to pull the tub back out and you might even need to chip some of the concrete away to allow yourself room enough to put a T in that pvc.

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    In the Trades mtcummins's Avatar
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    Can someone explain to me why we're putting a Tee into the vertical PVC? Or a P-trap at all? Am I seeing the picture wrong, or is that PVC drain not vented and there's already a trap below grade?

    If its possible to extend that PVC up and tie it into the vent, its probably a good idea, if not code required (someone else can chime in on that, I never do shared vents... don't know the code for them). Then you'd need a Tee to tie in the drain and get a vent.

  6. #6
    DIY Senior Member dlarrivee's Avatar
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    He asked how to connect a p-trap without creating an s-trap...

  7. #7
    Test, Don't Guess! cacher_chick's Avatar
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    Quote Originally Posted by mtcummins View Post
    Can someone explain to me why we're putting a Tee into the vertical PVC? Or a P-trap at all? Am I seeing the picture wrong, or is that PVC drain not vented and there's already a trap below grade?

    If its possible to extend that PVC up and tie it into the vent, its probably a good idea, if not code required (someone else can chime in on that, I never do shared vents... don't know the code for them). Then you'd need a Tee to tie in the drain and get a vent.

    We cannot see if there is a trap on the bottom of that riser. If there is, then the installer failed to install a proper vent for the tub.

    If there is not, then a sanitary tee will need to be cut into the vertical pipe so that the trap can be installed and the vent can continue upwards.

  8. #8
    In the Trades mtcummins's Avatar
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    So unless I'm seeing the picture wrong (there's no vent on the tub line and there's already a trap below grade), let me rephrase...

    Why are we telling the OP to put 2 traps on a drain line, and then leave an open top on a Tee?


    Edit: Previous post was posted while I was typing, didn't see it until after posting reply.

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    DIY Senior Member dlarrivee's Avatar
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    What is so confusing for you? Who said that there was already a trap?

    The original poster wants to know how to install a trap, why would he be asking if there already was one?

  10. #10
    In the Trades mtcummins's Avatar
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    Quote Originally Posted by dlarrivee View Post
    What is so confusing for you? Who said that there was already a trap?

    The original poster wants to know how to install a trap, why would he be asking if there already was one?
    I did. Look at the picture. Its not possible to be sure from this picture, but I'd say its 80% chance that there's a trap buried in there. I've said twice (and now 3 times), to correct me if i'm wrong, but the picture sure looks like there's a trap. What's so confusing about this statement? I know the OP said he's adding a trap, I always look at the pictures to confirm, and I'm doubting the need for one, so it seems imprudent to advise how to add a 2nd trap before determining that there is in fact not one already there, as it appears.

    There is also apparently no vent on the tub... the picture clearly shows 1 vent and the tub line is just a stub-out. I won't advise on the legality of this setup, as I don't ever do this (I vent every fixture), but that seems to be the situation. Therefore, advising a Tee makes no sense w/o determining that there is in fact to be a vent. The OP even said that the vent (indicating only one) was on the sink.

    This rough-in looks like a 2" lav vent wet venting the tub, with a PVC trap buried below grade on the tub. The reason the rough in is not in the wall is that the tub is meant to drain straight down into the rough in. Its a bit off though, so I think all that is needed is 2 45s to offset the line a bit, and a trap adapter to accept a tailpiece.

    Please correct me if I'm wrong on any of this, but I don't see the point in advising someone based on what they asked when the pictures seem to show otherwise.

  11. #11
    DIY Junior Member blackm3sedan's Avatar
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    I'm not sure if there is a trap at the bottom of the riser. I should have taken better pictures, but at the time, I was just thinking of documenting where the pipes are run and not what they looked like.

    I thought it would be a bad idea and and very unusual to bury the trap in the 20" thick footer, so I'm assuming it's not there. If the trap is there, then I doubt it meets my plumbing code for having the trap within 24" vertical distance of the fixture drain. I'm trying to get the 'licensed" plumber that did the install to come back out and take a look at it, but I'm getting the run around from him. He claims his company doesn't do rough-in plumbing work and didn't do my install. I only believe one of those statements.

    It's going to be difficult to vent that fixture without using an AAV. The bathroom is installed under a nearly flat roof, only 6 degree pitch, and the tub installs in the lowest corner of the roof. I'd have to put an access panel for the AAV on the outside wall, since it would be behind the shower wall. But I hate even more the idea of putting a vent through a flat roof.

    Since the sink is tee'd into the main line before the tub is, doesn't that also vent the tub? The vacuum created by the toilet flush will be relieved as it passes the tee for the sink and should prevent it from pulling water out of the p-trap. The overflow for the tub should also vent that line also, even if it's not recognized by code.
    Last edited by blackm3sedan; 12-07-2011 at 05:14 AM.

  12. #12
    Plumber jimbo's Avatar
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    Thank you for staying with us on this. I can't tell from the angles of your photos if there is sufficient height for the trap to already be there. Frankly, it would have been "usual" for the plumber to put one there. You need to dig down deeper in that tub box to find out whats what.

    What's wrong with a vent on a flat roof? I think FL is under the IPC which apparently would allow an AAV. Under the UPC inspectors often do not allow an AAV just to make your life easier! They insist on proper venting.

  13. #13
    Test, Don't Guess! cacher_chick's Avatar
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    This isn't rocket science- pour water down the standpipe and shine a flashlight down to see if there is a trap holding water. If there is not a trap, the line will drain clear.

    Quote Originally Posted by blackm3sedan View Post
    The overflow for the tub should also vent that line also, even if it's not recognized by code.
    The overflow is ahead of the trap, and does nothing to prevent the trap from being siphoned.
    Last edited by cacher_chick; 12-07-2011 at 08:17 AM.

  14. #14
    DIY Junior Member blackm3sedan's Avatar
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    Quote Originally Posted by cacher_chick View Post
    This isn't rocket science- pour water down the standpipe and shine a flashlight down to see if there is a trap holding water. If there is not a trap, the line will drain clear.



    The overflow is ahead of the trap, and does nothing to prevent the trap from being siphoned.
    Hey, easy on the rocket science stuff. I work for NASA.

    Now that you mention it, there is water in the bottom of the riser. But I also know the small tank is full of water, because I tried to move it. I'll get power to the pump to clear it and see if the water is still there.

    So if there is a trap at the bottom of the riser, then all I have to do is connect the white pipe to the black pipe, right?

    Am I going to have problems in the future with the trap being lower than 24" beneath the fixture drain, assuming the inspector doesn't catch it? Is that some silly code requirement with no technical reason for it?

  15. #15
    DIY Junior Member blackm3sedan's Avatar
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    Well it does appear that there is a trap at the bottom of the riser. Either that or it's sloped the wrong way. There is definitely water sitting in the bottom of the riser after the pump is activated. I guess the only way to be sure is to dig it up, hoping that it's not buried in the footer.

    So am I ok in just connecting the tub to the riser without a trap. Do I NEED a vent? I was a little worried about slow draining without the vent, but I think the overflow should be enough of a vent for that (which is what I meant in my previous post).

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