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My wife wants to build a small add-on to the house in the current carport for the washer/dryer. It's not a huge project. The washing machine will be about 30ft from it's current location. I don't want to run plumbing outside the house to the drain; I'd rather do it through the attic, which extends over the carport. My question is: how do I handle the water discharge? Someone told me that the discharge head on a washing machine water pump is enough to handle the rise into the attic and the run to the drain, but I haven't really been able to find out if that is true. My original thought was to install a small holding tank with a float switch operating a small 110V Jabsco pump.

If I go the holding tank route, does it matter how the holding tank is installed in relation to the washing machine and what would be a "safe" minimum size for the holding tank? Surely 10 gallons would suffice?

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up vote 6 down vote accepted

In homes where there are no drain lines in the basement floor, it's common practice to use some form of cistern containing a pump. A quick search at Home Depot turned up the SANISWIFT®, made by a company called Saniflo. The specifications list this unit as having a vertical discharge of 14 ft., which should be more than enough.

I've seen similar setups in many basements, where the only drain available is overhead.

enter image description here

Grey water from the sink and washer are collected in the cistern, then pumped up and out of the area when the cistern is filled to a certain level.

If the washer discharges faster than the grey water pump can handle, you're going to have problems. That's why when installing a system like this, the cistern should always be large enough to hold more than the volume of water that will be discharged by the washer. In the above image, the sink acts as a secondary reservoir (as well as an air gap) allowing the pump extra time to discharge the water. If you're not using a sink it's a good idea to have a larger cistern, and/or a grey water pump that can handle the volume.

You'll also want to install a check valve, on the discharge line from the grey water pipe. This will prevent the water in the vertical pipe from draining back into the cistern, and causing a potential infinite loop situation.

As for whether or not you should rely on your washing machine discharge pump to lift the water, you might find this related question useful.

WARNING:
This is only appropriate for grey water discharge. This method is NOT appropriate for sewage discharge.
Obviously there are other manufacturers of other systems, and you could always build you own system. I do not recommend or endorse this product, it is only used as an example. Searching for grey water pump will find many alternative products.

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Thanks very much. –  Mark Petitfils Jun 4 '13 at 15:57
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I would not even think about pushing the washer water to the attic. That is a disaster waiting to happen. Water goes down. You have two choices. Get the water over to the main stack - I am not sure of your setup but if you have a basement this is usually doable. The second option is to pump it out to the yard. Since this is not waste you can pump to the outside - you can ask local building inspector about local codes on this.

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Not sure what you mean by main stack. Are you talking about the original washing machine drain? That's my goal is to move it to that drain. –  Mark Petitfils Jun 2 '13 at 17:00
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+1 - I totally agree that trying to pump the water from either the washer OR a holding tank is almost like carrying around a loaded mouse trap. Plumb it correctly and be happy. Note that getting it plumbed correctly may very well be a factor that defines just how you go about locating and executing on this project. –  Michael Karas Jun 2 '13 at 18:34
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I have helped a few people put washers in the garage/carport. The city always let us pump the washer water out to yard. They treated it the same as a outdoor faucet. Not sure the plumbing code behind it. –  DMoore Jun 2 '13 at 18:42
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Also one we popped holes in the PVC once it hit a few feet out of carport... Water drained into the side flower bed. Drilled about 40 holes - the beginning ones were about 1/8 inch and towards the end I think we worked up to about 3/8 inch –  DMoore Jun 2 '13 at 18:47
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