(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 10 of 10

Thread: Slope requirement on 3" horizontal drain - 1/8" or 1/4" per foot? Drain design?

  1. #1
    DIY Junior Member Kubota_Kid's Avatar
    Join Date
    Sep 2012
    Location
    Shelton, WA
    Posts
    3

    Default Slope requirement on 3" horizontal drain - 1/8" or 1/4" per foot? Drain design?

    One source specifically states that horizontal 3"+ drains require 1/8" slope (< 3" require 1/4" slope). Another source says 3" drains require 1/4" slope. I am installing a 3" drain under slab that will accomadate a 1/2 bath in a shop. The main 3" drain will run approximately 26' before it enters the septic tank. Do I go with 1/8" or 1/4" slope?

    My design is to start the drain with a 3" closet bend. Down stream 2.5' from the bend I will install a 2" to 3" waste T with the 2" entrance at the top. From the waiste T the main 3" drain continues straight for 23' to the septic tank. At the waste T I will use a 2" long sweep 90 degree elbow that I will run horizontally from the waste T for approximately 2.5' before using another 90 degree long sweep elbow which will send this 2" wet vent/drain pipe vertical in order to drain the sink and vent the system. Comments or suggestions would be appreciated.

    Thank you,

    Kubota_Kid - Shelton, WA

  2. #2
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,655

    Default

    IT depends on which code is used in your area. But, one error is that you CANNOT use a sanitary tee in a horizontal line.
    Licensed residential and commercial plumber

  3. #3
    DIY Junior Member Kubota_Kid's Avatar
    Join Date
    Sep 2012
    Location
    Shelton, WA
    Posts
    3

    Default

    How would you connect the 2" wet vent/drain into the horizontal drain down stream of the closet elbow? Thanks. KK

  4. #4
    Plumbing Contractor for 49 years johnjh2o1's Avatar
    Join Date
    Aug 2009
    Location
    South*East
    Posts
    1,121

    Default

    Use a Y and 45.

    John

  5. #5
    DIY Senior Member kreemoweet's Avatar
    Join Date
    Sep 2009
    Location
    Seattle. WA
    Posts
    371

    Default

    There are no "sources" that matter other than your local plumbing code. As near as I can tell, that would be the 2009 Uniform Plumbing Code, possibly
    with local amendment. I don't have that version handy, but a somewhat earlier one states that 1/4" per foot is the minimum slope required for ALL drain piping,
    provided that 4" or larger pipes, under some unusual circumstances, and with prior approval of the local authority, can have as little as 1/8" fall per foot.
    Nothing prevents, and in some cases it would be desirable, to have greater slope. I have found that it is always desirable to have greater than 1/4" slope
    when running pipe in a trench, and for any distance.

  6. #6
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010
    Location
    Maine
    Posts
    2,942

    Default

    Does Washington allow wet venting? I believe its UPC which unless it's been amended, does not allow wet venting.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  7. #7
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,655

    Default

    UPC has ALWAYS allowed wet venting, if it is done properly. If he is using the IPC, they would probably allow 1/16" slope if someone asks for it.
    Licensed residential and commercial plumber

  8. #8
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010
    Location
    Maine
    Posts
    2,942

    Default

    UPC in Maine DOES NOT allow wet venting. IPC minimum pitch for pipes 3" and larger is 1/8 ipf.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  9. #9
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Location
    Bothell, Washington
    Posts
    14,202
    Blog Entries
    1

    Default

    UPC Washington State allows wet venting for a bathroom group. ( No kitchen sink, no washer )
    1/4" per foot grade or better.
    Wyes on the horizontal.

  10. #10
    DIY Junior Member Kubota_Kid's Avatar
    Join Date
    Sep 2012
    Location
    Shelton, WA
    Posts
    3

    Default

    Just want to say thank you for all of the post. Very helpful. When I first browsed this site I was impressed by the professionalism of the questions and responses. A great group of folks. Thanks again. KK

Similar Threads

  1. Anyone use an angle finder to check for 1/4" per foot slope?
    By JoshRountree in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 11
    Last Post: 09-01-2011, 06:10 AM
  2. Vent size for 3" horizontal drain from water closet
    By techinstructor in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 14
    Last Post: 08-12-2011, 07:43 PM
  3. 3" trap arm - horizontal drain height change
    By Rousifier in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 4
    Last Post: 02-19-2011, 08:31 PM
  4. Splicing into 3" PVC horizontal drain line
    By PharmD in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 18
    Last Post: 10-09-2010, 01:56 AM
  5. 1/8" toilet drain slope issue with picture
    By KSHandyMan in forum Toilet Forum discussions
    Replies: 2
    Last Post: 06-20-2007, 01:31 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •