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Thread: Bathroom sink floor drain vs wall drain

  1. #1
    DIY Junior Member VermontRemodeler's Avatar
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    Default Bathroom sink floor drain vs wall drain

    Good day everyone,

    I'm working on a house (built in the 30's) that is being gut renovated, and the plumbing has just been roughed in. I'm about to get started on the bathroom and I see that the plumber has kept the sink drain on the floor. From what I understand, I can use an elongated P trap before making the turn to connect to the floor drain to avoid an S trap situation, but this setup would seem to limit vanity choice with the additional piping. The wall that the sink is being installed on is an interior wall with vent access.

    Are floor drains still often used for sinks on this type of full remodel? Isn't it generally better practice to run the drain into the wall if there are no issues preventing it?

    Thank you very much in advance, I really appreciate the advice!

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    In a sense, all drains go through the floor.

    You cannot have a code-approved sink drain going down, unless you have a vent going up.

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    DIY Junior Member VermontRemodeler's Avatar
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    Quote Originally Posted by cacher_chick View Post
    In a sense, all drains go through the floor.

    You cannot have a code-approved sink drain going down, unless you have a vent going up.


    Yes all drains go through the floor in one manner or another... i'm asking specifically about one that essentially goes straight down from the sink...

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I don't think code approves of a p-trap on a sink being beneath the floor. Also, there's a maximum drop, even when installed above the floor (but not a big deal, I think it's 24" and unless the sink is very high, easily attainable). Regardless, to keep it from being an S-trap, the vent must come off of the vent arm or at the point where the waste turns down. SO, since the vent must go up, the conventional place for the trap and trap arm is just underneath the sink, which is normally easy to accommodate with a vanity.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Moderator & Master Plumber hj's Avatar
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    If the drain goes "down" beforfe its vent, it IS an "S" trap, regardless of any machinations you do to try to avoid it.
    Licensed residential and commercial plumber

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    DIY Junior Member VermontRemodeler's Avatar
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    Simple and straight forward HJ, thank you.

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    In the Trades Gary Swart's Avatar
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    You say the room is gutted, so putting the drain in the wall wouldn't be too difficult and certainly would meet code.

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    Moderator & Master Plumber hj's Avatar
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    A more important question ,might be, "What kind of plumber installs a sink drain "in the floor" these days?" Two answers come to mind. A "cheap one", or a "lazy one'.
    Licensed residential and commercial plumber

  9. #9
    DIY Junior Member VermontRemodeler's Avatar
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    Quote Originally Posted by hj View Post
    A more important question ,might be, "What kind of plumber installs a sink drain "in the floor" these days?" Two answers come to mind. A "cheap one", or a "lazy one'.
    I see, confirms my suspicions. Thanks again.

    So If I don't move the drain to the wall, and it has to be vented before (or when) the waste turns down, does that mean I have to have either use an aav (if allowed) under the vanity or run a 1.5" vent through the wall to meet up with the stack?

    Thanks yet again... And do you guys have Terry Love t shirts? I'd order a few!
    Last edited by VermontRemodeler; 02-16-2013 at 07:03 PM.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Yes, and either way it would have to be done properly.
    Licensed residential and commercial plumber

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