Dishwasher installed with drain below floor no high loop

tumbuluJanuary 9, 2009

I had my dishwasher relocated as part of a kitchen renovation and it has never worked well since - I finally had a service call today and was told it need a standing drain pipe 20 inches above the floor - right now it has a drain under the floor in the basement. Is there anyway this is a valid installation? I get the impression the plumber took a shortcut that just never could have worked, but would like to know if there is some way this arrangement is workable. I plan to contact my GC to ask him to get a plumber here to fix this - any advice? Also - do you think it is reasonable to hold the GC accountable for the plumbers shortcut? I did report this issue to the GC months ago, but he looked at it and said it was getting plenty of water, so must be an issue with the appliance (adviced a service call from appliance shop without either of us realizing that the problem was the plumbing). Should the GC have known this DW was improperly installed? I'm hoping he will fix it using a plumber who knows how to do this, shouldn't any plumber know this is how you install a DW?

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Is the dishwasher drain "through" the floor to the basement? My dishwasher also drains through the floor to the basement. It has it's own line into the main sewer line. My husband is the plumber and it's not a shortcut! It's a lot more involved to do that vs. drilling a hole in the side of your cabinet and punching out the garbage disposer hole for the hose to drain (I'm assuming you have a disposer?) If your dishwasher isn't next to your sink, then that's why the plumber probably did it that way...the 20" stand pipe makes no sense since most DW hoses are usually floating around inside the kitchen sink cabinet and the hose usually isn't 20" high??

    Bookmark   January 9, 2009 at 10:36PM
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I know Bosch requires a high loop. I am not sure about others but with a Bosch you will no have good results if you do not have the drain looped high.

    Bookmark   January 10, 2009 at 10:21AM
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What brand dishwasher do you have? You might want to post on the plumbing forum.

    Bookmark   January 10, 2009 at 12:19PM
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thanks for responding - I appreciate any advice/comments. I have found the installation manual.. (Maytag) and it looks like this is a valid approach, and probably due to the fact the dw is not adjacent to the sink. It appears to be missing an air gap. according to installation manual if the drain is going into a p-trap beneath the DW floor, it requires an air gap. I don't really understand what this is.
There is a hole drilled from the basement right below the DW, so the water hose going in and the drain hose are through that opening, the drain hose then is routed to a p-trap nearby but it is indeed also accessed from just below the floor. When the appliance man was here, we let water fill the DW, then we opened the dw and watched it drain out. He indicated that with proper install, the water would not drain unless it was pumped out by the dw drain pump.
do you think I need an air gap ? Is this something a plumber can do? very involved? thanks so much for your advice

    Bookmark   January 10, 2009 at 6:49PM
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You need to post on the plumbing forum for Lazypup's attention and he can quote the applicable plumbing code for you, but the short of it is that no DW should connect directly to the sewer system. It should connect via an approved indirect connection before the P trap on your sink or to the dispsal, or else have a separate stand pipe like a laundry does. There are also regulations covering how close to the drain the P trap has to be (no puttingin a P trap in a basement for a fixture on the first floor, etc.) This is all part of the plumbing code for health and safety reasons.

    Bookmark   January 10, 2009 at 7:34PM
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An air gap is really an air "vent". If your drain line is far away from the main sewer than you need an air gap so the air will help the water drain.

What problem are you having with your dishwasher? It sounds like the water is draining and not filling to wash? I think an air gap would help the water drain, not keep it in the dishwasher?

Live wire oak, plumbing codes are different throughout the country. When I said my husband was the plumber I mean he is a Registered Master Plumber, not just a do it yourselfer. Not only is the trap for the dw below our kitchen floor in the basement, so are the two traps for the drain lines for the double kitchen sink, which is within the plumbing code where we live. When I said directly into the sewer, there is a trap on the line, but after the trap it has it's own pvc drain line into the sanitary sewer...we have a storm sewer also.

    Bookmark   January 11, 2009 at 12:29AM
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Isn't the most reliable method to consult the dishwasher manufacturers installation instructions for proper guidance?

The initial post indicates the machine is a Maytag. They have a website where documents can be searched, if the hard copy instructions can't be located.

    Bookmark   January 11, 2009 at 9:01AM
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I agree. Start with what the DW manufacturer says. Call them too.

Dishwasher manufacturers know that all their products will send the drain water uphill a few inches (to a High Loop or to an AIr Gap). Therefore, I conclude, they have put pumps in that drain water by sending it that high as a normal course of operation.

Therefore, I conclude, it might cause too much water to be drained if the drain hose is sent downhill upon leaving the DW instead of up first for a local high spot. Too much water being pumped out could mean the water seal is open instead of blocked by water.

Plumbers will tell you that water dropping too fast to a P trap down too low can cause the P trap to siphon itself out, and this too can break the water seal, opening the line to sewer gases.

The manufacturer will say something about this. Some will spell it out that the drain hose has to go "high " first before going down to the P trap, and some haven't written that out but will still say so over the phone.

I'd call the manufacturer instead of relying on internet strangers.


    Bookmark   January 11, 2009 at 2:11PM
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You need either an air gap or a high loop. What is happening is the wash water is syphoning out. This is not good.

    Bookmark   January 11, 2009 at 2:37PM
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A Miele DW will work in that type of install no problem.

They are $$$


That type of install may not meet code in your locale.

    Bookmark   January 13, 2009 at 8:50PM
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I have an older DW. On mine, the tube comes out around the bottom rear of the DW and loops around an indented space around the back of the unit, where the hose clips in place. The tube goes up one side around the top and then is free on the other side This is how you get a 20" height because a DW is approx 24" tall (i.e. cabinet height). Then in my case the tube connects to the Garbage disposal but could easily just connect to a drain in the floor.

    Bookmark   January 14, 2009 at 11:07AM
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Thanks for all the responses - I did find my installation guide - it appears this is a valid installation (drain below the floor) but I read that what is missing is an airgap. I do have a garbage disposal under my sink -but this drain is not directly connect to that. I really don't know enough about plumbing to see what is wrong - just know it is draining the water out as soon as the water is fed in. I have a call in to my builder - hope he will respond and send a plumber to review the setup and address this.
I do appreciate the input I've got here and on the plumbing forum. I'll update when I have some response from a plumber who sees this and fixes it.

    Bookmark   January 14, 2009 at 12:48PM
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This is also why the Universal Plumbing Code and other building codes that regulate plumbing mandate the maximum distance between a fixture and the P trap that serves it. (That's why no P traps in a basement below a fixture. They have to be directly and very close to the fixture they serve, or a standpipe created.) Even a small amount of water can reach a fast enough velocity to completely clear the P trap if it's too far from the fixture it serves. No water in the P trap equals sewer gasses in the home. Combine that with no high loop on a DW, and you have the potential for a very nasty health and safety issue.

    Bookmark   January 14, 2009 at 2:20PM
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