One of the problems with the washing machine surge tank greywater strategy is that what you are watering has to be downhill of the machine. This is a common problem with greywater systems, and trying to use pumps to get the water uphill is simply not economical, nor is it environmentally hip since those pumps have a lot of plastic and other icky industrial materials in them.
Fortunately washing machines have a pump built-in and it’s possible to use your washing machine’s pump to get water both uphill and a reasonable distance horizontally. Unfortunately, washing machine pumps are not designed with this in mind, so you run a slight risk of burning out or decreasing the life of your washing machine’s pump should you attempt to move the waste water out to your garden. There are, however, ways to minimize the risk of pump burnout.
The guru of greywater, Art Ludwig, suggests the following methods for using your washing machine’s pump to irrigate plants:
1. Use only 1 inch HDPE or either rigid or flexible 1 inch PVC pipe. Smaller pipe may burn out the washing machine’s pump and larger pipe will allow water to accumulate and get stinky. Standard garden hose is not a good idea because of the risk that it will kink and burn out the pump, however flexible 1 inch PVC can be easily substituted.
2. Every 50 horizontal feet of run equals the same amount of pressure as running 10 inches vertically. Ludwig suggests limiting the combined horizontal (using the 50 feet = 10 inches formula) and vertical run to the equivalent height of where the water would normally empty out into the standpipe near the top of the machine.
3. Install a three way valve at the standpipe to allow diverting the water to the sewer.
4. The pipe may need to be vented (either by running a vent pipe up or using a swing check valve as a vent) if the end of the pipe is lower than the water level in the washing machine. This is to prevent an unintentional siphon that could empty the washing machine before its cycles have completed. This is apparently not a problem with all washing machines.
5. It’s best to get the pipe up to its highest point early and then run down from there though it is possible, since the water is under pressure, to run pipe up, down and up again. Having sections of pipe where water will stagnate, however, runs a slight risk of the aforementioned stinkiness, and burst pipe in places where it freezes.
6. Installing a swing check valve close to the washing machine will prevent water from flowing back into the machine should you be moving a flexible hose around and lift that hose above the level of the machine.
7. Rig up a bypass to somewhere the water can flow if you live in a place where it freezes. This is not a problem for us in sunny LA.
8. Since the water is under pressure it’s possible to rig up fancy distribution systems in the garden. For ideas on this see Ludwig’s book, Create an Oasis with Greywater.
9. Lastly, a note to our rentin’ homesteaders–this is a greywater strategy you may be able to get away with. And if you burn out the pump, and the machine is owned by the landlord, you’ll be sticking it to the Man!