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    Maximum trap distance?

    Asked May 22, 2011, 01:41 PM 6 Answers
    Is there a maximum horizontal distance that a trap can be from the drain?

    I have a mid-60s bi-level house that has a cantilever on the upper section. As shown in diagram #1, the original shower base extended over the cantilever and the trap was right under it. I gutted the bathroom and replaced all the old copper drains with PVC. The new shower base will be in the same location, but I need to use a trap with a clean out. The clean out would not be accessible if it is placed in the cantilever. If I do the set up as in diagram #2, the trap would be approximately 15" from the drain. The trap would still serve it's purpose (I think), but I need clarification on the distance as if it would cause any problems that I can't think of. Thanks

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    6 Answers
    Milo Dolezal's Avatar
    Milo Dolezal Posts: 7,155, Reputation: 519
    Plumbing Expert

    May 22, 2011, 02:05 PM

    The first drawing is fine. If you have only 15" between trap and vertical drain than you are OK. In my area we can run 2" pipe from trap up to 48" to the vertical transition. Since pipe will be buried inside overhang, use glue trap and glue all other joints along the way. Support horizontal pipe (dirt arm) with 2 straps: one as close to the trap and the other 2/3 of the length away. I assume vent is there and you will be reusing it. Install Clean Out on the vertical pipe and directly above San Tee.

    Hope that helps. Back to you. Milo
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    hkstroud's Avatar
    hkstroud Posts: 11,931, Reputation: 899
    Home Improvement & Construction Expert

    May 22, 2011, 02:44 PM

    I think he wants to do option 2. Probably so trap won't freeze. Unfortunately that amounts to a running trap.
    shader's Avatar
    shader Posts: 235, Reputation: 12
    Full Member

    May 22, 2011, 04:31 PM
    I never had a problem with the original trap freezing. The main reason to move the trap is the one I planned on using has the small clean out on the bottom-threaded cap & gasket. Maybe my terminology for "clean out" was incorrect as the plumbers call it.

    Milo-using 2" drain and the vent is right inside. If I go with your set up, I assume the clean out would give me access to the trap if it had to be snaked.

    Hk-what is a running trap? Sounds like that's not a preferred method.. Thanks guys
    ballengerb1's Avatar
    ballengerb1 Posts: 27,379, Reputation: 2280
    Home Repair & Remodeling Expert

    May 22, 2011, 04:42 PM

    A running trap is what you drew in your pic #2, just a trap in the middle of a horizontal run of a drain. How many times in your life so far have you had to use that small cap on a trap? Been doing this for over 45 years and my 1/2" drum snake is quicker and better.
    hkstroud's Avatar
    hkstroud Posts: 11,931, Reputation: 899
    Home Improvement & Construction Expert

    May 22, 2011, 06:16 PM

    I'm with Bob. Do you really need the trap with the clean out? Granted if you have ladies with long hair the trap will periodically get clogged with hair. Far easier to simply remove the drain cover, stick a wire clothes hanger down it, twist a couple of time and pull out the clog.
    The clean out will let you drain the trap and possibly pull out some clog. Won't let you snake through it, too small
    argaiu1017's Avatar
    argaiu1017 Posts: 92, Reputation: 8
    Junior Member

    May 22, 2011, 06:59 PM
    1st of all in line traps on 2nd picture are illegal and never done.
    2ndly your only allowed 5' of trap arm on 2" drain that is from trap to drain. the reason is u create an s-trap, that means the weir of trap is above opening of vent. if u install 1/4" per foot on drain @ 5', that puts your weir above tie in drain. If you had a negative pressure on your drainage the trap would siphon and cause sewer gases to enter house. 1 1/2" drain is 42".
    U could install picture 2 but, you would be asking "why is sewer smell in my shower?" goodluck

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