Drainage for two sinks and two dishwashers

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Icerabbit, Jan 5, 2016.

  1. Icerabbit

    Icerabbit New Member

    Joined:
    Jan 5, 2016
    Location:
    Maine
    I am seeking some input for a kitchen island remodel, where due to countertop changes new cabinets and plumbing became necessary. Nothing lines up new - old. Trying to simplify and minimize / avoid drilling more holes in the rafters below.

    Old setup from the seventies.
    Two sinks, two dishwashers. Each with 1 1/2 drain via a drum, going as two arms into a single 2" inch waste line which about ten feet furter drops down five feet into large cast iron. The drum barrel for one of the dishwashers were not in use anymore and they emptied into a disposal. The other one lacks the always recommended high dran loop.

    I was hoping to simplify this and have each dishwasher emptying into their adjacent sink.

    As the center of the island is open and servicable (made access panels) and not tiled, just an extra layer of plywood, I was hoping to use that void as a service corridor for all water, drain and electrical. (Versus drillng through cabinet bottoms and worse tile flooring)

    So I could see 1 1/2 below the sink, p trap into center of island, then run 2x two inch down 10 feet over to the cast iron, with cleanout offset at the end off the 10 ft line etc.

    But space is limited as rafters are 12 on center. The old setup seemed ok with a single 2" line. And no p traps in any cabinet, only drums under floor. ( no lnger code as i read it)

    So my most simplified idea became, mixing old and new:

    1x 2" 10 ft line to center of the island, 2" p trap under the floor, 2" coming up in the void with two wyes of 1 1/2 that go to each sink plus dishwasher and high on top of that 2" pipe, unone of those new air admittance valves.

    I have looked at code and been concerned with the DFU load where dishwashers and sinks each are counted as two units, even though never three or four would be emptied at the same time.

    I also can't find confirmation if I can run a single 2" p trap under the floor, vs two 1 1/2 p traps under the sink or the floor. Or is a p trap under each sink now mandatory. In old island plumbing reference code it was stated p traps had to be under the floor for venting purpose. I'd be very happy to that, more room in the cabinet.

    Additionaly some web stuff points to that I would need to run 3" horizontal, come up with three inch in the center of the island and two inch under each the sink. To me this seems overkill since there's no bath or toilet involved ... and the old setup was fully functional.

    Additionally here s refernce to right sizing vs upsizing because one needs the scouring and flushing through action of any possible particles, ... That would just cling on if one were to oversize.

    Thank you for reading and any recommendations and references people may have.

    I am hoping to keep it simple and functional; think my idea should work but would hate to make a mistake or have to tear it out later due to some practical oversight or code issue.
     
  2. CountryBumkin

    CountryBumkin Active Member

    Joined:
    Sep 4, 2009
    Location:
    Orlando, FL
    Can you post a picture of your current setup?
     
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  4. Icerabbit

    Icerabbit New Member

    Joined:
    Jan 5, 2016
    Location:
    Maine
    Thank you for your reply.

    Envision a 3x3 cube square = nine squares roughly 24x24 each, but with a hollow center.
    The dishwashers are on two corners, adjacent to a sink that is in a middle square.

    I don't have pictures of the old setup, but I did sketch this out. Slightly simplified perspective wise, as the one sink is offset a bit deeper, behind the dishwasher. The four units of two sinks and dishwasher are basically an L: sink, dishwasher, sink, dishwasher.

    [​IMG]
     
  5. CountryBumkin

    CountryBumkin Active Member

    Joined:
    Sep 4, 2009
    Location:
    Orlando, FL
    The drawings help. I'm not a plumber - and I'm sure someone with the knowledge will be by soon.
    But I think you need to have the vent "after" the trap. Where is the vent located for the original (as built) setup?
     
  6. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I have limited knowledge, but I know the P traps cannot be below the floor. They need to be before the vent(s) in the path.
     
  7. Smooky

    Smooky In the Trades

    Joined:
    Apr 4, 2011
    Location:
    North Carolina
    The trap arm should not be more than 24 inches below the sink outlet. Drum traps are not allowed.
    1002.1 Fixture traps.
    Each plumbing fixture shall be separately trapped by a liquid-seal trap, except as otherwise permitted by this code. The vertical distance from the fixture outlet to the trap weir shall not exceed 24 inches (610 mm), and the horizontal distance shall not exceed 30 inches (610 mm) measured from the centerline of the fixture outlet to the centerline of the inlet of the trap.

    1002.3 Prohibited traps.
    The following types of traps are prohibited:

    1. Traps that depend on moving parts to maintain the seal.
    2. Bell traps.
    3. Crown-vented traps.
    4. Traps not integral with a fixture and that depend on interior partitions for the seal, except those traps constructed of an approved material that is resistant to corrosion and degradation.
    5. "S” traps.
    6. Drum traps.

    Exception:
    Drum traps used as solids interceptors and drum traps serving chemical waste systems shall not be prohibited.
     
  8. Icerabbit

    Icerabbit New Member

    Joined:
    Jan 5, 2016
    Location:
    Maine
    The original setup, as built had no immediate vent ( only vented via the main house stack ... The 10 ft island drain pipe drops down five feet in the basement into the cast iron mian line ) and was the correct way to vent an island back in the day. I have found a couple older code references that for islands the stand pipe way of doing things (as built) with a p trap below the floor was 100% A OK and the way to go without adjacent vent.

    Thank you smooky,

    I know drum traps as built are now prohibited. Did not intend to yse them. I found them suspect to clogging the first time I saw them.

    Is there still some exception for islands? As old code had it ...

    Based on your info / the code, can I do a 1 1/2 sink p-trap under each sink with the special under sink t-piece for a dishwasher ... That connects to sch40 1 1/2 and out 2".

    Or am I forced to squeeze four p-traps in??? RE: each plumbing fixture shall be i...

    ... Because code compliant examples of a dual sink, plus disposal and dishwasher examples 1 under sink trap ...
     
  9. Smooky

    Smooky In the Trades

    Joined:
    Apr 4, 2011
    Location:
    North Carolina
  10. Smooky

    Smooky In the Trades

    Joined:
    Apr 4, 2011
    Location:
    North Carolina
    SECTION 409
    DISHWASHING MACHINES

    409.1 Approval. Domestic dishwashing machines shall conform to ASSE 1006. Commercial dishwashing machines shall conform to ASSE 1004 and NSF 3.
    409.2 Water connection. The water supply to a dishwashing machine shall be protected against backflow by an air gap or backflow preventer in accordance with Section 608.
    409.3 Waste connection. The waste connection of a dishwashing machine shall comply with Section 802.1.6 or 802.1.7, as applicable.
    SECTION 913
    ISLAND FIXTURE VENTING

    913.1 Limitation. Island fixture venting shall not be permitted for fixtures other than sinks and lavatories. Residential kitchen sinks with a dishwasher waste connection, a food waste grinder, or both, in combination with the kitchen sink waste, shall be permitted to be vented in accordance with this section.
    913.2 Vent connection. The island fixture vent shall connect to the fixture drain as required for an individual or common vent. The vent shall rise vertically to above the drainage outlet of the fixture being vented before offsetting horizontally or vertically downward. The vent or branch vent for multiple island fixture vents shall extend to a minimum of 6 inches (152 mm) above the highest island fixture being vented before connecting to the outside vent terminal.
    913.3 Vent installation below the fixture flood level rim. The vent located below the flood level rim of the fixture being vented shall be installed as required for drainage piping in accordance with Chapter 7, except for sizing. The vent shall be sized in accordance with Section 916.2. The lowest point of the island fixture vent shall connect full size to the drainage system. The connection shall be to a vertical drain pipe or to the top half of a horizontal drain pipe. Cleanouts shall be provided in the island fixture vent to permit rodding of all vent piping located below the flood level rim of the fixtures. Rodding in both directions shall be permitted through a cleanout.

    [​IMG]
     
    Last edited by a moderator: Nov 14, 2017
  11. Icerabbit

    Icerabbit New Member

    Joined:
    Jan 5, 2016
    Location:
    Maine
    Thanks for all the input.

    Interpreting the above, I need a P-trap in each sink cabinet (which I thought originally) and a clean-out in the vertical part. No double P trap situation so I omit the accessible one under the floor in open basement.

    So I should be able to proceed with the following, more conventional setup ... I hope? Yes? No?

    [​IMG]


    PS: I don't like the idea of the sanitary T where it seems stuff can flow left-right-left with those small curved branches, hence I would use 2 WYE above one another where stuff comes in at 45 degree angle and cannot move across. Otherwise I'm going to be back to doing two vertical drain pipes ... and more trickiness under the floor.

    Again thanks for looking at this!
    Really appreciate the help.
     
  12. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    You need sanitary tees to allow air to go from the vent to the trap arm. Alternatively, you could put an AAV on each trap arm before each wye.
     
  13. Smooky

    Smooky In the Trades

    Joined:
    Apr 4, 2011
    Location:
    North Carolina
  14. Icerabbit

    Icerabbit New Member

    Joined:
    Jan 5, 2016
    Location:
    Maine
    I can see how that makes sense regarding air movement. I was concerned about ideal water flow and angles.

    Is there a particular model?

    As on the co.lincoln.wa.us site there is a pdf top ten DWV mistakes ... which I'd read a while back and got me concerned about that fitting. Are they simply talking about directional mistake?

    Re: top ten plumbing mistakes: installing a sanitary t instead of a wye or long sweep for drainage connection or back to back fittings (sinks) not directional

    It would be horinzontal to vertical, proper direction ...

    I have seen the AAV per arm example, but they're a bit expensive and one can handle both sinks.
     
  15. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    A double fixture fitting.
    1.5" on three sides and 2" going down.
    Add a 2" cleanout below the fitting. Those trap arms are very short anyway and not likely to be the issue. (Unless you have an old disposer that doesn't chip the food you put down.)
     
  16. Icerabbit

    Icerabbit New Member

    Joined:
    Jan 5, 2016
    Location:
    Maine
    Thanks, Terry, for your reply and your wonderful forum!
    Also again thanks to all the helpful people here who take time to help a weekend warrior solve his puzzle!

    I will get that fitting tomorrow!

    Locating the cleanout ...

    Does it have to be below? Or can it be above?

    I have some space and height concerns (cabinet base, deep sink, disposal exit height, p-trap ) but think I can make either work.

    I guess I though above as that's a guaranteed dry spot and figured that would push down through the joining fitting.
     
  17. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    Above is fine if you have the room.
     
  18. Icerabbit

    Icerabbit New Member

    Joined:
    Jan 5, 2016
    Location:
    Maine
    Thanks a ton!

    Cleanout high and drain a bit lower might work easier, but you can bet I will mock it up twice and measure three times before I start drilling holes, cutting, glueing etc.

    Once again many many thanks for this wonderful forum to you and all its contributors! You guys are champs! And very patient! :)
     
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