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Old 11-11-2008, 10:42 PM   #1
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Washing Machine Drain

We have a 40 year old house and the washing machine drain is essentially just a PVC pipe that goes to the central drain that connects to the kitchen sink. You can not even run the dish washer at the same time or there will be back up.

At any rate, there is not a pipe that goes through the roof for air intake (I do not know what this is called) so the washing machine drain can tend to over flow. It has done this more often lately for some reason.

Is there a maneuver option I can put in place to make sure the drainage is consistent and enough air gets in to let it flow properly, other than making the PVC huge? It is about three inches in diameter with a height of about three feet now. If I make it taller it will obscure a window and look absurd.

Is there a plumbing piece that will act like an air valve at the bottom or something to help the flow?

Am I even making sense? lol

Here is a pic of what I mean:


Last edited by mqcarpenter; 11-11-2008 at 10:50 PM. Reason: Add pic
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Old 11-12-2008, 11:04 AM   #2
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My first impression is that there is a clog in the drainline. Washers put out a lot of lint into the lines. Can you see the piping that the line from the washer goes into, maybe from a crawl space or basement? You said there was no line going out of the roof? This is called a vent. If it isn't going through the roof, it terminates in an attic. Not good at all since it can fill this space with sewer gas. Please check on this. I have included a link (just click on it) that shows a basic drain and vent system. The washer is in the basement here. Newer codes are requiring a 2" drain for washing machines since the newer models have much stronger pumps. Extending the 3" line will not solve your problem.



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Old 11-12-2008, 12:58 PM   #3
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Good info. Thank you. I will look for a clean out section first. Looking at that diagram, it may join to the neighboring kitchen sink in terms of the vent. This section of the house is slab and there is no basement so I can not visibly see what is going on. Just outside that wall is an overflow cap though, so I will see if it is clogged maybe?

It sounds like my newer washer might be causing this though, based on your pump comment. I never thought of that but the capacity is fairly large so maybe combined with lint in the line and a large amount of water, it is just too much for it.
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Old 11-20-2008, 07:47 PM   #4
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It seems like your drain pipe reduces from 3" to 1". Is this correct? If so your drain pipe should be 2" PVC. That would definitly cause slow drainage and backup, especially with newer model washing machines, they pump out about 20 gallons a minute! I would access the wall behind the machine, and see if there is a p-trap on the line(there should be a 2' P-trap some where). If the line is not vented you can either cut in a vent before the p-trap and take it up through the roof or use a stooder vent(spelling?) also called a mechanical vent, by simply cutting in a 2"x1"1/2 tee gluing it in vertically and gluing the mechanical vent on to the 1"1/2 outlet of the tee. Code requires the mechanical vent to be accessible, so installing a access panel in the drywall at point of vent is a good idea.
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