Long horizontal drain pipe run clogging regularly

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by SWB, Jul 11, 2005.

  1. SWB

    SWB New Member

    Messages:
    9
    Location:
    Louisville, Kentucky
    We're having problems with our kitchen sink drain pipe. It's a double sink, and the dishwasher also hooks into the drain. After the trap and going into the wall, the 2" PVC drain pipe heads down vertically about 2 feet to our basement. At this point, it makes a right angle and heads about 16 feet horizontally, then makes another right angle and heads another 14 feet horizontally, where it finally meets a 4" vertical drain pipe. The kitchen sink and dishwasher are the only fixtures on the 30-foot run of 2" pipe. The 2" pipe has been clogging regularly since we bought the house a couple of years ago, causing water to back up in the kitchen sink, especially when the dishwasher is running.

    Since it happened the first time, we've been trying to keep the pipe clear by running hot water for a few minutes every couple of weeks down the pipe, avoiding using the garbage disposal (putting solid stuff in the trash, instead), etc., but the pipe continues to clog.

    My guess is that 30 feet is far too long for a horizontal run of 2" pipe, and gunk is settling in the pipe and stopping up the works. However, I don't see a straightforward way to add slope to the run. The 16-foot run does have some amount of slope to it (probably at least 1/4" per foot, but I haven't measured it), but I can't tell whether there's any slope on the 14-foot section.

    Does 30 feet sound too long for a horizontal run of 2" pipe, or should it work just fine provided that a 1/4" per foot slope is maintained? Would it help to move to a larger diameter pipe? Is it possible there's just something wrong with the current pipe and replacing it with new pipe would fix the problem? Is there some kind of pump or other device I can insert to help move things along without clogging? Any other ideas?

    Thanks!
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Minimum slope on a 2" line is ¼" per foot, so a 30 foot run should slope 7½" from one end to the other. This is your problem.
  3. SWB

    SWB New Member

    Messages:
    9
    Location:
    Louisville, Kentucky
    Okay, that's what I figured. I finally went down to the basement and actually measured the slopes. I also took a few pictures to illustrate the situation.

    This is the first length of pipe, which is about 16 feet long with a slope of about 0.2"/foot (flow is towards the camera):

    [​IMG]


    The pipe then drops down & turns 90 degrees via a 90-degree and 45-degree elbow (flow is to the left):

    [​IMG]


    The second length of pipe is about 14 feet long with a slope of about 0.1"/foot (flow is away from the camera):

    [​IMG]


    The run finally meets a 4" vertical pipe and heads down (flow is towards the camera):

    [​IMG]


    The average slope over the entire 30' run is about 0.28"/foot, but of course most of that drop takes place in the 90/45 elbow construction.

    The question now is, what can i do about it? To me, it looks like I need to raise the start of the 16-foot section and lower the end of the 14-foot section. I'm guessing this will require replacing and rebuilding the entire 30-foot run of 2" pipe, as well as replacing and rebuilding much of the upper 4" structure that it connects into. Is there a better or easier solution?

    Thanks!
  4. SWB

    SWB New Member

    Messages:
    9
    Location:
    Louisville, Kentucky
    Transparent PVC

    I just discovered transparent Schedule 40 PVC. As I make whatever repairs are necessary, I'm considering inserting a few short lengths of transparent pipe in strategic locations to aid in diagnosing any future clogs. Other than the higher price, are there any negatives to this approach? Is the transparent stuff fully compatible with the primers and cements used with white pipe? This would mean using a few couplings between transparent and white pipe in places that would otherwise be smooth, continuous pipe. Is that okay, or am I asking for trouble? Any good sources other than McMaster-Carr?

    Thanks!
  5. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,351
    Location:
    Yakima WA
    I am not familiar with clear PVC, but if it is true PVC, then use PVC cement and primer. I also have never heard of McMaster-Carr, but any building or plumbing supply will have PVC pipe. I don't think you need the clear stuff, but it won't hurt anything to have it and you will have peace of mind knowing you have good drainage. The real fix to your problem is to get enough slope.
  6. jrogers99

    jrogers99 New Member

    Messages:
    7
    I'm new here and maybe this is way off base but I see the problem simply as a vent problem. When your run of pipe (30 feet in your case) drops more than it's diameter (2") it needs to be revented to move waste. From reviewing the pictures I'm not seeing any reventing. Could this be the problem?
  7. PEW

    PEW DIY Senior Member

    Messages:
    487
    "average slope" will give you misminformation. A long flat section or bellied section will lead to problems, even with an acceptable "average slope".

    Paul
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    pipe

    Most "transparent" pipe has a thicker wall than standard pipe. If that is the case with the pipe you are looking at, then your "solution" will become your problem as material gets caught against the thicker pipe and creates a clog. From your description, you may be able to revis, or create a new connection, at the terminus and then just rehang/regrade the pipe.
  9. SWB

    SWB New Member

    Messages:
    9
    Location:
    Louisville, Kentucky
    What I have in mind is to cut off and cap the existing wye connection to the 4" pipe. Then insert a new wye to connect the regraded pipe to:

    [​IMG]

    Any problems with this approach?


    That's true; there is no reventing.

    Is that true regardless of how the drop occurs? In my case, almost all of the drop happens suddenly at the 90-degree turn:

    [​IMG]

    I can also envision a long, constant-slop pipe eventually dropping more than its diameter, but in my case, the two constant-slope sections have very little slope.

    If I need to add a vent, where (and how) should I add it? The situation is complicated by the fact that the space above is completely open (vaulted/cathedral ceiling); there are no walls leading to the attic space until the pipe reaches the far side of the stairway near the 4" vertical. You can see the furnace vent heading up this wall in first photo of this post.


    Yep, I should'nt have mentioned it ... I calculated the "average" slope out of curiosity, but it's not relevant and may be confusing the issue. Please ignore. :)
  10. casman

    casman New Member

    Messages:
    78
    Location:
    New York
    Although I'm not a pumber your proposed drawing/pic is the same setup I am running and I've never had problems with it clogging. Hopefully it's ok cause I've never heard of doing a revent thing cause of the 2 inch diameter drop post and if true then mines wrong as well....
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    pipe

    You do not have to "revent" the pipe.The only vent you need should be in the wall where the sink drain connects to the vertical pipe.
  12. plumguy

    plumguy New Member

    Messages:
    192
    Location:
    MA
    It definately looks like you can fix that run by lowering the wye like you show in the pic. Just remember that 1/4" per foot is not the minimum, it is the pitch you want. Too much pitch can be just as bad as not enough.
  13. SteveW

    SteveW DIY Senior Member

    Messages:
    1,052
    Location:
    Omaha, NE

    How can too much pitch be harmful?
  14. plumguy

    plumguy New Member

    Messages:
    192
    Location:
    MA
    Let's use a toilet drain as an example. On a horizontal run pitch greater than 1/4" the solids could be left behind and the water will flow without carrying them downstream and obviously solids left will eventually contribute to a blockage. In theory and engineering design 1/4" per foot is the correct pitch for water and solids to evenly flow downstream.
  15. Cal

    Cal New Member

    Messages:
    228
    Location:
    Northern Virginia
    I can barely make out that the 90 turning up to go to the kitchen sink looks as if the "cup" is tight to the underside of the floor.That sets the start of the first long run.So getting slope from that 90 across the ceiling and still staying on top of the duct is most likely too flat. (Sorry,all of the above is obvious just recapping)Can you cut the line under the kitchen sink and open the hole around the 90 under the floor, thus raising the starting center point ? Is it a traditional vent,island vent or in-line vent ? I KNOW this is stupid,,,,Has it been snaked ? By the way ,,,the 3 x 2 wye on the vertical stack is a GOOD idea.
  16. plumguy

    plumguy New Member

    Messages:
    192
    Location:
    MA
    I can't see the 90 either and would hope it is a long sweep. But, I think "recapping" gives him a majority vote on minimal work to help with the problem. "Has it been snaked" If it continuosly clogs I would imagine it has.I'm sorry,but I don't think it is an island sink ( and how would that matter?) it looks like it "turns up" above a foundation on a outside wall, plus, I think you would see the bow (loop) vent next to the drain! . And I'm just curious what is the difference between a "traditonal vent" and "in-line vent".
  17. Cal

    Cal New Member

    Messages:
    228
    Location:
    Northern Virginia
    Plum,

    I just meant can he see the venting under the sink or is it a vent that runs up inside the wall. I am very fond of these new in-line ( Studor model) vents.
    It would be nice if he could just re-run the entire line and be done with it.
  18. plumguy

    plumguy New Member

    Messages:
    192
    Location:
    MA
    Hey Cal, I hear you. I thought that might be what you meant, but I guess it depends where you are from! Those mechanical vents are illegal here in MA and are not an option. So, sometimes it makes you approach a job or problem differently. I myself would rip it out and replace it, considering the cost of pvc and being a short run.But, it comes down too one's budget and ability!

    But, that it is why a forum like this can be so valuable and interesting!
  19. toolaholic

    toolaholic General Contractor Carpenter

    Messages:
    874
    Location:
    Marin Co. Ca.
    where,s all the missing hangers

    who signed that job off? :confused:
  20. toolaholic

    toolaholic General Contractor Carpenter

    Messages:
    874
    Location:
    Marin Co. Ca.
    mechanical vents arn,t allowed in ca. either

    only with inspectors permission and have to be accessable not buried
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