Results 1 to 3 of 3

Thread: Washing machine drain without trap or vent ???

  1. #1

    Default Washing machine drain without trap or vent ???

    Hi - I posted this on another thread but did not get any responses. I would really appreciate any comments here.

    I have a 45 year old house. The washing machine discharge backs up over the drain pipe. I will be snaking out the discharge branch to the main.

    However, this has me concerned --
    it appears that the washing machine drain does not have a trap or a vent.

    I will confirm this when I return to the house in a week. I will remove some drywall to expose the pipes. My first look was through drywall cutouts which gave limited visibility.

    Was it accepted 45 years ago to install a washing machine drain (2" cast iron) that would not have a trap and not be vented??

    It appears that the 2" drain pipe goes down to the crawl space without a trap and without a tee to a vent. The drain makes a horizontal jog through one wall stud. It is remotely possible that there is a trap at that point, but I don't think so. It is behind drywall that I did not rip out yet (I looked with a mirror and flashlight through the drywall cutouts -- I don't think there is a trap). If there is a trap, it is about 10" below the drain pipe inlet. Is that enough drop from the inlet or should the trap be moved closer to the floor?

    After the horizontal jog (of about 10"), the drain pipe drops down through the floor plate into the crawl space. There is no tee to a vent. In the crawl space, the 2" drain connects to a 4" sewage branch that runs about 20' to a 6" sewage pipe. The 6" pipe runs out of the house toward the street. The 20' of 4" cast iron is only used by the washing machine drain, nothing else drains into that entire 20' branch.

    If there is no trap, then the drain pipe may act somewhat like both the drain and the vent (as long as the washing machine hose is not connected air tight), correct?? Is this an approach that may have been likely 45 years ago? Has anyone seen anything like this before?
    It bothers me not to have a trap. Would 20' of 4" pipe serve to buffer or hold sewer gases at bay?

    Any comments or suggestions (assuming the drain is not trapped or vented) -
    it has been this way for 45 years -- leave well enough alone??

    Do I HAVE to add a trap and vent (or am I grandfathered in)?
    Does anyone recommend that I change things even if I am not required to?
    If I add a vent, does it have to go through the ceiling and roof? Could it just go up in the wall (an exterior wall behind brick with drywall on the interior side) and stop short of the plate (then potentially allowing sewer gas into the exterior wall cavity)?

    I appreciate any comments.

  2. #2


    A vent is required to serve that washer drain. However this vent must be placed on the downstream side of the trap. Purpose of a trap is to allow air into the drain so weight of water does not suck the trap dry. Your trap must be outletted above the washer drain stand pipe. May use an air admittence valve is placed always accessible.

    If it were me I would cut out all that old half full cast iron and use rubber boots to covert to new plastic drain pipes the entire length. Over time this old cast iron will collect crap to the point of plugging half full even if you rod it.

    Washer drain stand pipe may be 1 1/2" but the trap and all plumbing down stream must be 2".

    Hope this helps


  3. #3

    Default trapless insert

    There is anew product on the market that can help. The trapless insert. It stops odors. Pro-Set Plastics has the patent they can direct you to some one close that may carry it.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Washing Machine drain without trap or vent?
    By jimrotten in forum Plumbing - Existing Home
    Replies: 1
    Last Post: October 12th, 2005, 10:43 PM
  2. basement shower drain for washing machine
    By mattmeister in forum Plumbing Codes - Residential
    Replies: 2
    Last Post: May 28th, 2005, 03:31 PM
  3. drain for washing machine in basement
    By Joe in forum Plumbing Codes - Residential
    Replies: 1
    Last Post: March 29th, 2005, 08:30 PM
  4. Drain, trap, vent within 4'?
    By noel in forum Plumbing - Existing Home
    Replies: 3
    Last Post: January 5th, 2004, 07:23 PM
  5. Drain pipe fpr a wahing machine
    By imported_marako in forum Plumbing - Existing Home
    Replies: 1
    Last Post: July 9th, 2003, 01:41 AM

Posting Permissions

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