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Thread: 3" trap arm - horizontal drain height change

  1. #1
    DIY Junior Member Rousifier's Avatar
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    Default 3" trap arm - horizontal drain height change

    Ever mindful of the need to avoid siphoning the p-trap under my new shower, I think the maximum developed trap arm for my upstream 3" toilet drain is 12'. If that is the case, I have a 3" height adjustment to do as the new location crosses over a 4" line that is that much higher. Does making a height adjustment with two 22 1/2" ells affect the allowable length? The toilet is now 6' from the 2" vent. So, it would go about 2' from the toilet at 1/4" per foot, drop about 3", then continue into the existing drain, again at the approved slope. Does that make sense? Is it allowable under Canadian or other codes? Does there need to be something placed between the ABS pipes or can they rest one on top of the other?

    Thanks in advance for any assistance.

  2. #2
    Master Plumber-Gas Fitter shacko's Avatar
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    If I read you right you want to go OVER another line?, can't be done.

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    Plumber jimbo's Avatar
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    shacko raises the pertinent question: are you proposing to go "up and over" ?? A drain line MUST be continuously downward...it can NEVER go back UP in any way. Maybe a pic or sketch would help us see what you want to do

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    Test, Don't Guess! cacher_chick's Avatar
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    As I read it, he will run the trap arm at one elevation and then drop down 3" after it clears a different horizontal line.

    The maximum developed length is published with 1/4" per foot of pitch as the standard. A jog in the line as you suggest would be considered a broken vent, and not allowed here.

  5. #5
    DIY Junior Member Rousifier's Avatar
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    Default 3" trap arm - height adjustment





    I knew I should have attached either photos or a drawing, but there's no reasoning with me sometimes.

    So, what I want to do is move the closet flange to the right end of the excavation, but as you can see if I extend the vented 3" line, it needs to jump over the 4" drain that come off the main stack. In the alternative I suppose I could raise the 3" at the far left end, then maintain a 1/4" per foot across the top of the four inch line. But then I'd be crossing the line, something I've done several times in my life, just never with plumbing.

    I could raise the line with two ells at the left end, which would give me a straight shot to the new flange location.

    Does this assist? Thanks very much for your input.

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