Do I really need .25 inch slope for drain?

Discussion in 'General Plumbing Help' started by Nate848, Apr 28, 2019.

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  1. Apr 28, 2019 #1

    Nate848

    Nate848

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    Hello

    I am roughing in a drain in new construction and its about a 38 foot run of 2" pipe just for the laundry room washer and sink in the laundry room. I only can get about 4 inches of pitch/slope in the run. Do you think only have a .1/8th or .15 inch per foot of pitch is ok for a 2" pipe? I dumped a cup of water in and it drained fine but code says I need .25 per foot.

    Thanks
     
  2. Apr 28, 2019 #2

    UFGator121222

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    1/8” will work fine. Especially if it’s only grey water.
     
  3. Apr 29, 2019 #3

    Diehard

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    The code says 1/4"/ft for a reason.
    It may work fine for a while but the slower average velocities tend to cause build up and eventual blockage sooner.
    Why not use 3"?

    EDIT: Also keep in mind that you are sizing a drain pipe for a Laundry Room not a cup of water.
     
  4. Apr 29, 2019 #4

    UFGator121222

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    Again 1/8” will work just fine. Why use 3” when there is absolutely no need to and that doesn’t change the fall at all. You will have absolutely no problem with 2” and 1/8 of fall. Everyone does it if it is needed. Your washer had a pump that will be pumping water out also. 2” pvc can handle something like 21 fixture units and you are using about 5 fixture units so no don’t use 3” that makes absolutely zero sense. You will have no issues at all with 1/8” 2” pvc. Good luck with it and don’t sweat it because you had it right the whole time.
     
  5. Apr 29, 2019 #5

    voletl

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    GReynolds929 likes this.
  6. Apr 29, 2019 #6

    Diehard

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    The 21 fixture units you mention is for a 1/4" slope, not an 1/8" slope.

    In my mind there are plenty of reasons to use 3".
    1. It's required by the applicable plumbing code.
    2. It reduces the fall by 50%.
    3. Many large new washing machines can and do exceed the flow capabilities of the standard 2" systems.


    I wouldn't use the 2" even if there was sufficient room to install it at 1/4" slope.
     
  7. Apr 29, 2019 #7

    CT18

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    Some codes say washer boxes have to discharge into a 3" stack. Also make sure it is vented correctly.
     
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  8. Apr 29, 2019 #8

    frodo

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    Nate,
    If it were me, I would run a 3'' line horizontally at 1/8'' per foot
    turn up with a 3'' 90 degree bend.

    install a 3x2 bushing inside the 3'' 90

    come up vertical with a 2'' pipe

    the 2'' will fit inside your wall,
     
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  9. Apr 29, 2019 #9

    Nate848

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    thanks for the replies everyone
    thanks for the advice and everyone else.
     
  10. Apr 29, 2019 #10

    Diehard

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    I would not rely on an AAV(Air Admittance Valve) for a washing machine due to the potentially high discharge rates.
     
  11. Apr 30, 2019 #11

    chiraldude

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    Not sure I agree with the statement of high discharge rates. The last 3 washers I have owned were high efficiency units that never dumped more than 3 gallons at a time into the drain. The drain pumps were tiny and discharge was through a 1" tube.
    Can you even buy an 20th century type washer that dumps 20-30 gallons into the drain in less than a minute?

    As for the pipe, make sure you put in a cleanout in a spot that is easy to find and access. Also be meticulous about deburring cut ends. Lint will tend to collect on sharp edges.
     
  12. Apr 30, 2019 #12

    frodo

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    Whirlpool pumps at 15 gpm with the stand pipe at 30'' off the floor
    for each 12'' added to the stand pipe the gpm pumped rate is diminished by 1 gallon per minute
     
  13. Apr 30, 2019 #13

    Diehard

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    GE also states 15 gpm with a change of 1 gpm for every foot change.

    I am not basing the high flow rate POTENTIAL on my experience. I have a 30 year old Maytag. I am basing it on the numerous articles and peoples experiences.

    Apparently 12 to 17 gpm is not uncommon on some of the newer large machines.

    Here's one example on the subject...
    https://www.pmmag.com/articles/85477-it-s-not-the-plumbing
     
  14. Apr 30, 2019 #14

    chiraldude

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    I saw that article too but then I noticed it is dated June 8 2000
    Maybe it is true but I remember the washing machine my parents had in the 70' that discharged 20+ gallons at a time out of a 1 1/2" tube.
     
  15. Apr 30, 2019 #15

    Diehard

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    Yeah but of course the tube size doesn't represent the total gpm.(Are you sure the ID was 1 1/2"?)
    Would have to assume the newer high capacity, high discharge rates, going through a 1" hose, is at a slightly higher pressure.

    EDIT: I just looked at my hoses. I do notice that he newer ones have a much thinner wall but I don't think the hoses from the 70,s were 1 1/2". How did they get them in a standpipe?;)


    EDIT2: Just looked at the ID of my newest of the 2 hoses I have connected to each other. It has a 7/8" ID. I see on the web that some are showing 5/8" ID washing machine hoses.
     
    Last edited: Apr 30, 2019
  16. Apr 30, 2019 #16

    frodo

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    just my opinion based on years of experience

    if the washer is on a first floor outside wall, you stick the c.o out the exterior wall at 18''
    same height as the sewer machine.

    if it is on an interior wall. you install the clean out behind the washer/ dryer at a height of 48''

    you make the size of the clean out 2'' as per code
     

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