Dishwasher drain lines.

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Mae-Ling

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I am in the process of installing a dishwasher in my home. Because of the layout of the kitchen it will be 12 feet away from the sink on another wall. I can not run a vent line up inside this wall as it is the centre wall in an 1973 modular house.

Also because of a heat duct in the floor joists I can not run a 1 1/2" drain line in the 12" cabinet beside the dishwasher.

1. The main 3inch stack is 8feet away. Can I run the discharge hose with a high loop behind the dishwasher below my floor joists on the basement ceiling and wye straight into the main stack? This would come in below all the other plumbing fixtures (sink, lavatory, toilet, tub.)

2. What size of line - 3/4" or go to something larger?

3. Would I need a P-trap in this line. as the high loop keeps water in the pump which acts like a p-trap.

I have used loop vents and re-vents in the past and because of obstructions and layout these are not possible. I had also thought of an AAV vent in the 12" cabinet beside the dishwasher but because of the heat duct in the joist space directly below it that is not possible.

Thanks for any help.
 
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Mae-Ling

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Then can I take the 3/4 inch hose through the floor and tie into the 1&1/2" line with a p-trap in it?
Then run the 8feet to the main stack?
 
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Mae-Ling

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Dishwasher drain lines last.jpg
Here is a drawing of my idea/question.
Is this OK to do? Will the P-trap or dishwasher siphon out?

Thanks
 

Mae-Ling

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I realize with a bit more work I could run a re-vent.
Tie in a 1&1/2" line in the wall beside the 3" main stack. run that down and under the floor over to the dishwasher, tie in the 3/4" high loop line, then a p-trap, then into the main 3" stack.

Not sure which side of the P-trap the re-vent should tie in on, re-vent high loop P-trap or high loop p-trap re-vent (I think the second is right)

Here is a pic.

Dishwasher drainlines re-vent after P.jpg
 

Terry

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It's a bit hard to tell what your plan is here looking from the side.
Plastic pipe isn't very much and goes in quickly. Plumbers like to ensure that every fixture is vented in a way that prevents a siphon occurring. Spending $20 more is small potato's at this point.

If you plan on leaving a dishwasher drain in that comes in below the toilet, you will need to add a vent between the p-trap and the main stack.
 

Mae-Ling

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the $20 isn't the problem it's the ripping open of walls! Lol

If I understand correct the second picture I posted should be OK.

Yes the dishwasher will come into the main stack below the toilet.

have the vent (re-vent) between the P-trap for the dishwasher and the main stack.
On your picture my dishwasher would come into the main stack just below where the toilet does.
So I run a line from my main stack tee off and put in a vent that ties into the main stack above the 1st floor fixtures.
carry through with the 1&1/2" line put in a p-trap then my line from the dishwasher with a high loop.

Dishwasher drain line Terry Love.jpg

That square drop is supposed to be the P-trap!
 
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Mae-Ling

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If my above picture is not permissable another option may be a island loop vent in the wall. The dishwasher is going in front of a door that was closed off. So even though I can not go up through the top of the wall and put in a vent I can put an island loop vent in the wall where the door was. The beam under this may be an issue but I could also move the cabinets out 1 or even 2inches if need as I am building the cabinets and counter top.

My above picture would be the easiest.
 

Dunbar Plumbing

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Your pictures are showing a running trap, which in most states is illegal. High looping does not break the continuous flow of wastewater leaving the dishwasher. An Air Gap will.

12' is a very long run for this design when the maximum trap to vent distance on 1.5" is usually 3 and half feet.

Installing the plumbing incorrectly to save demo'ing a wall doesn't follow codes of any kind. You want a functional design.
 

Mae-Ling

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I agree, need to do it right.
Problem is that the wall the dishwasher is on is a center wall in a 1973 modular house. It is built in two halves so to speak. drywalll 2x4 on flat1/2" plwood on whole wall then another 1/2" plywood 2x4 on flat and drywall on other side of wall.So I can not go up through it with a vent to the roof. which was my original plan.

I think I need to think of this as an island with no sink. How would one plumb that? I am thinking a island loop and nipple from the P-trap to the dishwasher hose. I do not need air gap it is not required here.

http://www.google.ca/imgres?q=island+loop+vent&hl=en&sa=X&biw=1024&bih=651&tbm=isch&prmd=imvns&tbnid=KQNh67xCqGpdwM:&imgrefurl=http://www.askme********.com/plumbing/air-admittance-valve-loop-109435.html&docid=MHG6wJnFXu9MmM&imgurl=http://www.askme********.com/attachment.php%253Fattachmentid%253D3987%2526stc%253D1%2526d%253D1184446928&w=713&h=750&ei=Pz3mTr2kL4vciALqg6SiBg&zoom=1&iact=rc&dur=404&sig=104427575351854170151&page=1&tbnh=142&tbnw=135&start=0&ndsp=15&ved=1t:429,r:0,s:0&tx=18&ty=69

only thing is I would either put the loop in the wall (was a door there so I have room to go down just not up as there is a whole header system above the door and at the bottom edge of the rafters.) Or move the cabinet out up to 2" if necessary. As I am building the cabinet and counter-top I can do this.
 
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Mae-Ling

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What might be easiest is if someone could give me a diagram of how you would plumb a dishwasher in a island with no sink.

Thanks for all the help. I was a renovation carpenter for over 20 years and have plumbed a few dishwashers in my own homes and helping friends where there was a sink near. Just not one like this.:confused:
 

MTcummins

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I don't think there is anything wrong with your picture, other than that the trap is drawn wrong. You need the water to fall straight down from the D/W into a P-trap, not go horizontal, then through a trap. Thats the running trap, but it would be easy to put a P trap under the washer. If you put the 1 1/2" p trap directly under the back of the d/w and stub up a pipe into the space behind it, you could attach the discharge hose to that.

You need to attach the vent to the 1.5" drain line after the trap within 42" of the trap. The vent cannot tie into the stack below ANY fixture drain, so if there are 2nd floor fixtures, you need to get above the flood rim of the 2nd floor fixtures (generally 42" off the floor) before tapping into the main stack. Or, you can take the vent directly through the roof.

If you're really stuck, an AAV w/in 42" of the trap might be your best option. Just make sure its at least 4" above the trap.
 

Mae-Ling

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Dishwasher drain lines hopeful.jpg

OK after reading and looking at what I can do because of ductwork for the forced air heating in the floor joists here is what I hope will work.

Take the discharge hose from the dishwasher, do the high loop behind or beside the dishwasher, take it down through the floor, run it 2 feet horizontal to get over ductwork and into the top of a p-trap. then it is 7 feet horizontal to the main 3inch stack.

for the venting -
There is an existing 2" fixture vent line for the basement bathroom that I can access. This ties into the main stack above the fixtures on the 1st floor. I would Tee off this just below the floor joists and tie it into the drain line just before the p-trap.

Hopefully it is clear in the picture.
 

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Mae-Ling

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Just did more reading , saw that p-trap should not be so low under the floor as that can cause syphoning even with the high loop.

OK I believe a 24" tailpiece is the longest allowed so if the top of my p trap is right up against the floor joists which I can do if needed, would that work? On a dishwasher where do you measure to/ Where the hose comes out the back?
 
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Mae-Ling

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I can use a island loop if I can come up through the floor at 10" wide then use 45's to widen it to up to 30" wide. This would allow me to put the p-trap between the two upright pipes and behind the dishwasher.



dishwasher wide loop.jpg
 
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