Build a Washing Machine Greywater Surge Tank

After the shower, the next best source for greywater is the washing machine. Constructing what is called a surge tank with a fifty gallon plastic drum is the simplest way to reuse your washing machine waste water. Perfectly good water that would ordinarily just go down the sewer will instead water your plants after first spending a short time in the fifty gallon drum.

Temporarily draining your washing machine into a fifty gallon drum has two advantages. First, it allows hot water to cool and secondly it prevents siphoning mishaps and washing machine pump burnouts that can happen if you try to move the water directly to your garden through a pipe. Here’s how to create a surge tank:

1. Get ahold of a fifty gallon plastic drum. Most big cities, Los Angeles included, have businesses that resell used drums. Make sure that you get a food quality drum and not something that held toxic materials. The best kind of drum for this purpose is one that has a lid, both so that you can clean it out periodically, and to make it easier to fit the hose connection at the bottom.

2. Drill a 1 inch hole in the side of the tank at the bottom.

3. You will need to improvise what is called a “bulkhead” fitting in order to hook up the tank to a regular garden hose. Instructions for doing this can be found here. Seal the fitting with silicon. Connect this fitting with a standard garden hose and use a ball valve if you want to be able to hold the water in the tank temporarily. Remember that greywater quickly turns into black water if allowed to sit around for more than 24 hours, so use this water quickly.

4. Direct your washing machine’s drain hose into the tank. The hose must first go above the top of the machine before going down into the tank in order to prevent the machine from draining accidentally. Also, don’t make this connection airtight–the washing machine needs an air gap, normally provided by the loose connection to the standpipe to prevent waste water from siphoning back into the machine.

5. For a deluxe installation, use a three way valve so that waste water can be easily shifted back to the sewer line should the need arise.

6. Place the tank on bricks to increase water pressure.

7. Remember not to use washing machine waste water if you are washing diapers.

As always, for more detailed information on how to do this get Art Ludwig’s excellent book Create an Oasis with Greywater.

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