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    mwarney's Avatar
    mwarney Posts: 26, Reputation: 1
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    #1

    Sep 21, 2006, 04:42 AM
    Drain Slope
    I've heard 1/4" per foot and I've also heard 1/8" per foot is acceptable for waste lines. What is the ideal slope? Does it depend on pipe size or fixture type? (i.e. toilet vs sink)

    Thanks!
    RickJ's Avatar
    RickJ Posts: 7,762, Reputation: 864
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    #2

    Sep 21, 2006, 04:49 AM
    We've always used 1/4" and I've heard from many that this is the standard. I've never heard of 1/8" per foot.

    I'd consider going 1/8" per foot if it were a sink or other liquid only drain, but certainly not for a toilet.
    mwarney's Avatar
    mwarney Posts: 26, Reputation: 1
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    #3

    Sep 21, 2006, 05:00 AM
    Quote Originally Posted by RickJ
    We've always used 1/4" and I've heard from many that this is the standard. I've never heard of 1/8" per foot.

    I'd consider going 1/8" per foot if it were a sink or other liquid only drain, but certainly not for a toilet.
    Thanks for clearing that up. I'm not sure where I read it but somewhere I remember instructions to maintain between 1/8" and 1/4" per foot. A plumber once told me to have "Half a bubble" on the level.
    RickJ's Avatar
    RickJ Posts: 7,762, Reputation: 864
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    #4

    Sep 21, 2006, 05:04 AM
    I'd far more trust a ruler than a level for something as important as slope. You sure don't want to be re-doing it later.
    allozier's Avatar
    allozier Posts: 33, Reputation: 3
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    #5

    Sep 21, 2006, 03:43 PM
    I usually use 1/4 in per foot which equals about a quarter bubble on a nine inch torpedo level. But with these 1.6 flush toilets they sell these days I have found that 1/4 in tends to let the water go by and hold the waste back and eventually build up and stop up. So I tend to run a little less slope on lines with toilets on them. You might check with other plumbers to see what they think but it works for me.
    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
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    #6

    Sep 21, 2006, 03:56 PM
    When we rough in for drainage we just crack the bubble on a level. In all the hundreds of rough ins we have done in my area we have never had a problem using this method. Only once, when I put in a super market was I held to using a transit on the refrigeration drains. I consider half a bubble to be too much fall. Regards, Tom
    mwarney's Avatar
    mwarney Posts: 26, Reputation: 1
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    #7

    Sep 22, 2006, 02:58 AM
    Quote Originally Posted by speedball1
    When we rough in for drainage we just crack the bubble on a level. In all the hundreds of rough ins we have done in my area we have never had a problem using this method. Only once, when I put in a super market was I held to using a transit on the refrigeration drains. I consider half a bubble to be too much fall. Regards, Tom
    Thanks Tom, Any idea what that interprets to (in terms of slope per foot)?
    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
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    #8

    Sep 22, 2006, 06:53 AM
    "Any idea what that interprets to (in terms of slope per foot)?"

    I never really figured it out mathematically but my guess would be 1/8th inch to the foot. Cheers, Tom
    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
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    #9

    Oct 8, 2008, 10:52 AM
    Originally Posted by RickJ
    I'd far more trust a ruler than a level for something as important as slope. You sure don't want to be re-doing it later.
    Sounds complicated to me Rick,
    Would you explain how that goes for the rest of us. The only time I've ever used a ruler is when I was held to zero slope putting in super market reefer lines and had to use a transit to do it. Regards, Tom
    massplumber2008's Avatar
    massplumber2008 Posts: 12,780, Reputation: 1210
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    #10

    Oct 8, 2008, 11:03 AM
    By the way Mwarney...

    Plumbing codes in the USA mandate that pipes 3" and smaller get 1/4" pitch per foot minimum.

    Pipes 4" and larger can have a minimum 1/8" pitch per foot.

    If not on commercial job using a transit level to keep track of slope I take a 4 foot level and I tape a 1/2" block of wood at the very end of the level which is equal to 1/8" pitch per foot so that when I place the level on the 4" or 6" underground pipe, for example, and get a level reading from the level I know I have a properly pitched pipe for sure!

    Good luck!

    MARK
    afaroo's Avatar
    afaroo Posts: 3,998, Reputation: 251
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    #11

    Oct 8, 2008, 11:30 AM

    I got this from Google,

    Minimum 1/4" of fall per foot on 2" pipe or smaller.
    Minimum 1/8" of fall per foot on 3" or larger.

    1/2" per foot is Maximum.

    The above is just an Info, Thanks.

    John
    massplumber2008's Avatar
    massplumber2008 Posts: 12,780, Reputation: 1210
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    #12

    Oct 8, 2008, 02:52 PM
    Hi John...

    I believe you found the only exception to the rules I posted earlier.

    MUST be IPC code... all others that I know of require as I posted... 1/4" per foot 3" and smaller, 1/8" pitch per foot 4" and larger.

    Always seems to be some exception to every rule! I swear!

    I know I wouldn't go with only 1/8" pitch per foot on a 3" toilet line... just seems to be asking for trouble.

    Have good day all...

    MARK
    afaroo's Avatar
    afaroo Posts: 3,998, Reputation: 251
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    #13

    Oct 8, 2008, 02:54 PM

    I agrre with you that's why I said an Info only, Thanks.

    John
    fennecip's Avatar
    fennecip Posts: 5, Reputation: 1
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    #14

    Jul 13, 2009, 03:41 PM
    I too wanted to know the answer to this riddle of the "bubble". I took a 4' level and put it on a level surface, and elevated one end exactly 1 inch (1/4" a foot). It works out to 1/4 bubble, and with a 1/2 inch raise it "just cracked" the bubble (1/8" a foot).
    massplumber2008's Avatar
    massplumber2008 Posts: 12,780, Reputation: 1210
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    #15

    Jul 13, 2009, 04:43 PM
    Hi Fenniecp:

    If you want a 1/4" per foot of pipe and you are using a 4 foot level I believe it is easiest to tape a 1" piece of anything and read the 4 foot level as LEVEL each time you take a reading... then no guess work about where the bubble is... ;)

    Guarantees that 1/4" per foot every time (or 1/8" per foot if using 1/2" block on 4 foot level).


    MARK
    fennecip's Avatar
    fennecip Posts: 5, Reputation: 1
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    #16

    Jul 13, 2009, 04:52 PM
    Oh I absolutely agree, or use a 6' 2x4 with a piece nailed to the end. I was just curious what it worked out to.:)
    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
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    #17

    Jul 14, 2009, 06:09 AM
    RickJ
    Über Member Join Date: Aug 2005
    Location: Tortosa
    Posts: 7,310


    We've always used 1/4" and I've heard from many that this is the standard. I've never heard of 1/8" per foot.

    I'd consider going 1/8" per foot if it were a sink or other liquid only drain, but certainly not for a toilet.
    I sure hate to bump heads with va super mod but I can't let this pass.
    Let's talk about slope. Too little of it and the solids won't be carried as the water seeps out. Too much of it and the water drains so fast the solids are left behind.
    Most codes mandate, 1/4" for drainage pipes 2" and smaller and 1/8th for 3" pipes and larger.
    Ricks statement,
    I'd consider going 1/8" per foot if it were a sink or other liquid only drain, but certainly not for a toilet.
    was simply bassackwards.
    Sorry Rick! Regards, Tom
    downthedrain's Avatar
    downthedrain Posts: 1, Reputation: 1
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    #18

    Sep 21, 2010, 02:17 PM
    If you have got a line of sight between your Point A and Point B you can run a string a line between the two using stakes. Run the line 1' above the grade to make sure discrepancies in grade do not interfere with the line. Use a spirit level to make sure the line is level between both points. Measure the starting height at Point A and the distance between the two points. For a 3" pipe multiply the distance between the points by 1/4" and for 4" pipe use 1/8" (check local building codes to see if they deviate from this standard). Use that sum to measure down from Point B, making sure to add the 12" for the line height).

    Before backfilling make sure that the slope is uniform and even by using a spirit level. Take note of where the bubble sits and check for any points where the bubble is not sitting in the same position. Raise or lower these areas as needed. Take care that the underside of the pipe is sitting firmly on sand before backfilling.

    Too little slope will leave waste sitting and building up in your pipe and too much flow could make the water separate from the waste (especially on 'watersaver' type toilets) and cause the same problem. (On non-city sewer systems: septic beds, etc. too much pipe slope will increase the pressure on the tanks and force a higher flow rate then desired on your system).

    All the best!

    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
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    #19

    Sep 22, 2010, 07:17 AM

    Mark nailed it! Pipes 2" and smaller = 1/4" to the foot while pipes 3" and up require only 1/8th per foot fall. I use a level and just crack the bubble on the big stuff and give it a little more for the 2" branches.
    If I am held to zero slope I use a transit. Cheers, Tom

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