Laundry Gray Water to French Drain

I am planning a stand alone washing machine drain to a French drain buried in the back yard. My plan is to have a traditional 44" from the floor standpipe (2" diameter) which will have a 2" P-trap then go out the exterior wall and take a few 90 degree bends before terminating into 2 "Infiltrator" extra capacity drains buried in the backyard. The two Infiltrator sections have 62 gallon capacity each, so I think that should accommodate one washing machine, since I think the ground will drain some of the water away as the washing machine is running. I have two questions:
1) Do I need to be concerned about odor entering the house through the standpipe, since this will be in no way connected to the house sewer?
2) Should I install another P-trap with a short vent pipe outside along the exterior wall just in case the capacity of the Infiltrator drain is exceeded? My thinking is that the extra vent below the level of the standpipe will drain off excess drain water if the Infiltrator cannot handle the gray water, and the extra P-trap between the Infiltrator and the short vent outside will maintain the trap seal and avoid odors coming out of the short vent.

The California Plumbing code does allow for graywater systems, but the requirements are quite strict. I don't think it is as simple as the system you are describing, but this is not the type of thing you want to wing on your own. Because this is an enviromental and health/safety issue, the penalties for failing to have the proper permits etc are steep. I suggest you at least get a copy of the CA plumbing code and read up. Look for a plumber with experience witht this kind of system.

Thanks. I am in Arizona and our state allows (even encourages) gray water systems. There are general guidelines provided by the state Department of Environmental Quality, which I will follow. However, these general guidelines are for health/sanitation issues, like not allowing runoff of gray water to an adjoining property, no ponding of water, no open storage of water, etc.
I am only concerned about the practical plumbing matters - whether or not I will retain trap seal and avoid odors in the house, and whether a secondary outdoor trap (below the laundry standpipe level) is advisable to avoid potential overflow/backup out the standpipe in case of outdoor drain blockage.
There are no experienced gray water "plumbers" I can find. There are plenty of "green" advocates of using gray water, but no experts in plumbing entire systems. Those new houses which are plumbing gray water are doing it in conjunction with an entire house sewer system, which does not apply in my case.
I don't know how I got California in my avatar - I will have to change that.

After searching the web, I found a somewhat detailed design for a laundry gray water drain. It looks like there should be a vent line or auto vent where the gray water line leaves the house to prevent siphoning of the trap seal by the drain system. This design mentions that the air gap caused by the loose fitting washing machine drain line in the standpipe creates a vacuum break, but the air vent provides extra protection against siphoning. Other designs I have found suggest two separate standpipes, which I think more closely approximates the stand alone standpipe I am planning, since a second standpipe would not be connected to the house sewer.
Here is the link to the Santa Barbara design.
http://www.santabarbaraca.gov/NR/rd...mplePlanLaundrytoLandscapeGraywaterSystem.pdf
Here is how my location looks. I would put the air vent right after the first elbow exiting the house.

The air gap at the hose does NOT prevent siphonage, in fact it would cause, or at least permit, it without a vent after the trap. one major consideration for your 'project" is that the water will seep away, but all the lint and soap will stay in the receivers. Eventually, the entire surface and seepage surface will be coated and at that point you will either have to clean the basins, sometimes not possible depending on how they are made, or replace them.

fortop said:

Thanks. I am in Arizona and .

Click to expand...

I could swear that when you first posted, your profile said Los Angeles. Maybe it's the alzheimers!

There is a difference between grey water recycling and grey water disposal. In this case I would be damn sure that I checked with the local inspector before doing anything at all. As for a trap and vent, why bother with them at all? Since there is no connection to the sewer, the only odor that should come back is that of laundry soap. Just do the Hillbilly thing and dump the washer out the utility room window, it should eventually seep into the french drain LOL Your detergent may well be bio-degradeable but that process takes time and given the amount of soapy water a washing machine discharges you will end up as HJ said, with a slimy scummy mess in short order. My advice (which I'm pretty sure will be ignored) Forget about it. there is nothing at all "green" to what you want to do. It will cost you 10 times more than putting it into the sewer and it is a service problem just waiting to happen.

Thanks all for your input. The house is 60+ years old and the cast iron/galvanized drains are rusted and corroded/scummed up enough so that the load capacity of the house drain system is limited. Washing machines put out a lot of water in a hurry, and I am sure that repeated big loads from the washing machine would overwhelm the drain system, as has happened in the past.
I know that the proper answer is to break up the concrete floor, remove the old drains, and install new PVC or ABS drains, but that is an expense that can't be tolerated know, or likely forever.
I have neighbors who have been using the infiltrator system for several years with no adverse effect. If you look at the Infiltrator segments they are quite large (like 1/2 a drain culvert -16" X 48"). The drainage is mostly downward, then up and to the sides of the unit. I expect that someday the system will plug up, but I am hoping that it will last several years with normal use. Should that occur, the drain line can be cut and rerouted to provide a surface drain, which eliminates the scum issue. This should be about a $150 "experiment." I am looking for a good lint filter for the drain hose. I know lint is also a problem in septic systems.