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Thread: 3" Toilet Drain

  1. #1
    DIY Junior Member KShirriff's Avatar
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    Default 3" Toilet Drain

    I have a toilet drain on the 2nd floor directly above a 2x6 wall on the 1st floor. Can I run the 3" drain from the toilet flange straight down to the basement without any elbows at the top and tie into the horizontal drain line? I have a 2" vent tied into the 3" pipe about 18" below the toilet flange and vented up throught the roof. Someone said that they think this design might suck the water out of the toilet trap. Is this true?

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    That's a really long drop but it won't suck the toilet trap dry with a vent. Not sure if that would meet codes...just don't know.
    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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    Forum Admin, Expert Plumber Terry's Avatar
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    It doesn't matter whether it drops straight down or has a few bends.
    Hopefully the bowl "does" siphon when you flush. The fill valve refills the bowl after a flush anyway. I would have no problem with a toilet drain run straight down. Wait..........I've done hundreds that way.

    Last edited by Terry; 11-08-2012 at 05:52 PM.

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    DIY Junior Member KShirriff's Avatar
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    should I put an elbow in it and offset it over and then down?

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    DIY Junior Member KShirriff's Avatar
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    Here is a pic Name:  plumbing.jpg
Views: 98
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    DIY Junior Member KShirriff's Avatar
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    going to reroute the vent at a 45 degree

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    DIY Junior Member KShirriff's Avatar
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    Thanks Terry

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    Forum Admin, Expert Plumber Terry's Avatar
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    Running the vent for the toilet on a vertical or a 45 is a good idea.

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    DIY Senior Member wjcandee's Avatar
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    I was going to say that you could replace that combo with a Y for the vent, which is effectively what they are saying above.

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