Washing Machine Drain Under Kitchen Sink

detroittolaJanuary 25, 2014

I'm about to test this setup by running the washing machine. Who thinks this won't work and why? What you are looking at is 9 feet of 3/4" SCH40 PVC from the washing machine drain to the 1 1/2" PVC tee and then through the p-trap and out to the main drain line.

I don't like to violate code but sometimes it's the only reasonable option.


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I think you will have serious issues with suds lock in that long 3/4 inch PVC pipe. However, it will come down to you usage patterns and your specific application and equipment choice.

Is it a top load? Top load has to pass about 10 to 14 gallons per fill out that little tube fairly quickly. A front load may have only 5 to 8 gallons to get out. Had the horizontal tube been 1.5 inch or 2 inch, you would have a higher success rate.

If a top load, does it have neutral drain (pump all the way out before attempting spin)? Speed Queen does not have neutral drain and would have a tough time with this set up, it would burn out the belt quicker attempting to spin the load with water, might even eject water over the tub cover.

An old whirlpool top load would likely pop the splutch from overload over time, a time consuming repair for the average Joe, but at least the part is cheap.

You will definitely have more dry time as a result and more loads where the motor current detection software will keep it from going to top speed. If you have an electronic model with some flexibility you may be able to program a little more spin time. But be aware, spinning is generally what wears out the machine. If it had a default spin time of 5 min, changing to 6 min will take away about 20% of the expected machine life. Spinning wears the seal and bearing systems in particular as well as the pump, shocks if front loader, and pivot element if a top loader. High in rush currents are harsh on the motor if the load is high.

Siphon risk? Hard to say. Most units have a duck bill back flow preventer just downstream of the pump so that after the water leaves the pump, it can't return to the machine. But generally you want the outlet at the drain pipe to be above the top water line on the machine.

Your local inspector would likely not be very happy!

Good luck.


    Bookmark   January 25, 2014 at 4:43PM
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Thanks for the interesting info on the spin cycle and wear patterns. This is a ventless condensing washer/dryer unit so I'm not sure if that makes a difference as well.

It's a front load with a 3/4" drain hose. I was planning on running 1 1/2" pvc instead of the 3/4" but I just don't have the room behind the cabinets and dishwasher. I see my biggest risk being pump burnout due to excessive back pressure. It looks like pumps are about $50 so I'll roll the dice.

I agree that inspectors would kill me but I'm not doing anything unsafe. I only risk damaging my own unit since I'm on the bottom concrete floor over the parking garage.

I ran it through a test cycle and everything worked great. It didn't even back up into the sink.

Now I just need to figure out how to stop that PVC p-trap cleanout from leaking without having to cement it in.

    Bookmark   January 25, 2014 at 6:05PM
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You would be amazed at how well marine grade below the water line silicone sealant works. With limited pressure exposure the stuff can last years. I would add one of those drip/water detection alarms that some other threads have described and drop it in that little tub you have under the pipes.

With front load washer and HE detergent with careful detergent use, it may be OK.


    Bookmark   January 26, 2014 at 12:04PM
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Thanks laundryvet. I appreciate your honesty and helpful tips. Most contributors just quote the code and rip into me without really giving helpful advice. When it comes to electrical, I follow the code to a tee due to the potentially dangerous energy. There is no risk of injury to anyone from what I have done here. The only risk is the possibility of me destroying my washer drain pump.

    Bookmark   January 26, 2014 at 1:01PM
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Sophie Wheeler

Where the heck is the vent? Ther's a whole host of other issues as well.

Unlike the electrical code which originated within the building industry, the origins of the plumbing code are in health code. An improperly plumbed dwelling is more than an inconvenience to the user. It can make you and your neighbors ill.

Please get a pro in to do that properly.

    Bookmark   January 26, 2014 at 1:15PM
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I'm relying on the disposer to sink and the vented main drain line just inside the wall as vents. I will also have a siphon break on the dishwasher. I'm on the bottom floor in a condo with no washer/dryer hookups. I don't think any professional would touch this. I do not see any possible health hazard associated with this. I only see possible drain pump damage due to excessive back pressure on the washer drain line.

    Bookmark   January 26, 2014 at 4:20PM
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Update: So far so good. No leaks and no water backing up into the sink.

The manufacturer allows the drain hose to be as high as 96". Mine is currently at about 46". Maybe the additional 50" of water head drain pumping capacity is overcoming the added drain flow restrictions that I've placed in the system.

    Bookmark   January 28, 2014 at 1:36AM
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I just ordered the LG washer/dryer combo and will be needing to do the same as you under my sink. Which machine do you have and how is the machine, and the plumbing, working out for you?

    Bookmark   June 9, 2014 at 11:07PM
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Sorry for the late response but I haven't been back here in a while.

I have the WM3987HW model. I love it along with the setup. I have had zero problems so far. I have never even seen any water backing up into the sink or disposer.

I brush out and vacuum up the lint that collects on the door gasket after every wash to prevent the lint buildup issues that some have complained about and to keep the 3/4" drain line as clear as possible.

I wash on the hot cycle because I know that there is quite a bit of room temperature water that sits in the long water line due to the extra long hose I'm using.

It sits in a custom cabinet which I keep open during the drying cycle to prevent possible mold or wood damage.

Seeing as how ventilation wasn't really an option, I am happy and regret nothing that I did with this project.

    Bookmark   July 22, 2014 at 8:29PM
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