(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 12 of 12

Thread: drain pipe size and venting sink

  1. #1

    Default drain pipe size and venting sink

    My kitchen sink drain runs from one side of the house to the other where it connects to the base of the stack vent. The total distance is about thirty feet.
    I have two questions:

    1. Is the current 1.5" pvc pipe large enough or should I replace it with a two inch pipe? It drains a double sink with garbage disposal.

    2. The only vent it has is basically a loose drain connection from a washing machine that was once installed (rigged) in the kitchen for the previous owners, if you want to call that a vent.
    I'm going to replace the pipe. Over that 30 feet, does it matter where I tie in a vent assuming it needs a vent. I want to vent it as close to the stack as possible.
    Hope that makes sense.

    Thanks,
    Barry

  2. #2
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    Location
    San Diego
    Posts
    9,001

    Default

    You have a problem here. The maximum length of the trap arm...the pipe from the trap to the vent connector....under the UPC is 42" for 1" pipe, and 60" for a 2" pipe. You should fix that/

  3. #3
    DIY scratch-pad engineer leejosepho's Avatar
    Join Date
    Nov 2006
    Location
    200 miles south of Little Rock
    Posts
    2,474

    Default

    Quote Originally Posted by barryw
    1. Is the current 1.5" pvc pipe large enough or should I replace it with a two inch pipe?

    2. ... does it matter where I tie in a vent assuming it needs a vent. I want to vent it as close to the stack as possible.
    I had a similar situation before a complete re-do of our drain plumbing, and here is my own take on the matter:

    First, an 1-1/2" sink trap cannot possibly let enough water through fast enough to completely fill a sloping 2" line and keep it that way "to the last drop". Therefore, a vent to protect that trap from being siphoned dry by the sink discharge going through it is but marginally necessary, at most. However, and since "code" seems to require one, you might simply install one of those "AAV" one-way check vents.

    Second, "to vent it as close to the stack as possible" is neither a good idea nor necessary, and for two reasons:

    1) If the drainage from the sink actually *could* suck its trap dry, a vent at the other end of the line would not stop that;
    2) That stack should already be well-vented by other means, making another vent right next to it and in an incoming line redundant.
    Last edited by leejosepho; 03-16-2007 at 01:35 PM.

  4. #4
    Homeowner geniescience's Avatar
    Join Date
    Nov 2005
    Location
    humid summers hot, humid winters cold
    Posts
    2,152

    Default can't be, as written.

    barry

    you must be mistaken. perhaps you meant to write it the other way 'round.

    david

  5. #5

    Default

    Should there be a partial obstuction it will cause siphoning of the trap if you do not have the vent very close to the trap....preferably on a tee at the end of the trap....or very close to it.

  6. #6
    DIY scratch-pad engineer leejosepho's Avatar
    Join Date
    Nov 2006
    Location
    200 miles south of Little Rock
    Posts
    2,474

    Default

    Quote Originally Posted by Randyj
    Should there be a partial obstuction ...
    Ah! I had not thought of that.

    So much for my "marginally necessary", eh?!

    Oops.

  7. #7

    Default

    Ok I found a vent. There is a vent beneath kitchen sink running into the wall.
    I missed it because I checked the attic and basement when looking at the plumbing. The problem, I can't find any place where the vent ties into the stack, and there are no other vent pipes running through the roof.
    So, suppose the vent is there and it is vented properly, are there any issues with the 1.5" drain pipe that runs about thirty feet to the base of the stack vent?
    Thank you!

  8. #8
    Plumber Winslow's Avatar
    Join Date
    Dec 2005
    Location
    Hawaii
    Posts
    450

    Default

    Quote Originally Posted by barryw
    Ok I found a vent. There is a vent beneath kitchen sink running into the wall.
    I missed it because I checked the attic and basement when looking at the plumbing. The problem, I can't find any place where the vent ties into the stack, and there are no other vent pipes running through the roof.
    So, suppose the vent is there and it is vented properly, are there any issues with the 1.5" drain pipe that runs about thirty feet to the base of the stack vent?
    Thank you!

    The drain should be 2", at least that is what is required by the UPC. Especially with a disposer on the line.

  9. #9

    Default

    Alright. I will change the pipe and do what I have to do to get the vent right.
    Thanks again.

  10. #10
    DIY Junior Member kk's Avatar
    Join Date
    Mar 2007
    Location
    Eastern CT
    Posts
    5

    Default

    Trying to learn something here... supposing Barry's sink didn't have a proper vent - what would the correct thing to do be? Being as it's 30 feet away from the stack, how do you run a vent line? With an existing structure it seems like it would be close to impossible to run up and over to the vent stack, and running a new vent stack up in the kitchen could be a problem too.

    What do you do?

    -Keith

  11. #11
    Homeowner geniescience's Avatar
    Join Date
    Nov 2005
    Location
    humid summers hot, humid winters cold
    Posts
    2,152

    Default hypothetic

    hi keith!

    i think lee joseph 0 mentioned AAVs. Studors.

    david

  12. #12
    DIY scratch-pad engineer leejosepho's Avatar
    Join Date
    Nov 2006
    Location
    200 miles south of Little Rock
    Posts
    2,474

    Default

    Quote Originally Posted by kk
    With an existing structure it seems like it would be close to impossible to run up and over to the vent stack, and running a new vent stack up in the kitchen could be a problem too.

    What [did] you do?
    The situation with the drain line for our washing machine was like that, and I have resolved that dilemma to my own satisfaction by placing the trap right at the stack and running a sloped 2" drain line to there. The washer sits below the middle of an upstairs room and is not on an outside wall. So, and even if this is not "in the books" or whatever, I simply did what it took to make a safe, working drain.

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
  •