Multi-pump drainage system for basement clothes washer
Posted by Vince G. on February 11, 2004 at 20:32:12:
My wife and I have a house in Pasadena, CA with a small sub-basement currently housing a furnace and water heater. We are seeking to install our stacked washer/dryer in the basement to save space in the house and permit us more flexibility in remodeling our kitchen. The difficulty is that the main waste line for the house is just below the floor level, i.e., above the level of the sub-basement. I estimate that the vertical distance between the washer outlet and the drain line inlet is about 8 or 9 feet.

I read the recent posts a few days back on a similar project (), but my local building department informs me that they will require the following:

- a drain water storage tank sized to accommodate effluent from at least two wash loads (in other words, at least a 70 gallon tank since the manufacturer informs me that up to 35 gallons can be used in a single load including extra rinse cycles)

- two redundant pumps to pump gray water from the tank up into the main drain line for our house

- a check valve for each pump to prevent backflow

I do have a fine and reasonable plumber that I plan to use for the project but I would like to do the bulk of the planning on my own and order my own parts to avoid spending more than I have to. I would appreciate any constructive input on the following ideas:

1) The least expensive tanks I have found are polyethylene - rated for 140 degrees F. I can certainly adjust my water heater thermostat to prevent going higher than this threshold. Can anyone foresee a problem with this tank material?

2) To avoid simultaneous activation of both pumps, I propose using two 115V automatic submersible pumps set at different levels within the tank - one close to the bottom and the other set higher. I propose adding a check valve at the outlet of each pump and then merging the streams downstream of the valves to a single waste injection line. I understand that I will need one vent / standpipe for the tank, and another standpipe for the sewer line connection. Can these vent lines be merged into a common standpipe?

3) I don't have very many attractive options for running a new standpipe. The best idea appears to be running the standpipe upward through my existing basement stairway corridor. Assuming that it will be secured to the wall behind a handrail (to prevent the standpipe from being damaged by someone using stairs), does anyone see any problems with this idea?

4) I am concerned about proper pump sizing. Obviuosly, I will need enough head and flow capacity to elevate the drain water nearly ten feet, but I don't want a large pump to be starting and stopping too often since I expect that would shorten its life. Most submersible pumps I have found, however, are 1/4 horsepower and up. One model that looks promising is available at but I am certainly open to recommendations for other pumps. (For sizing purposes, it seems to me that a pump capable of flowing between 1 - 2 GPM at 10 ft of head should be sufficient, given that a 35 gallon wash cycle lasts about 30 minutes, for a net gray water generation rate of 1.17 gallons per minute.) Electronic actuation, rather than float actuation, looks more attractive to me due to potentially higher reliability.

5) I assume that ABS plastic pipe will be acceptable for connecting the various components. If there are other economical alternatives, however, please let me know.

6) I don't yet know where to find appropriate check valves. Any input would be appreciated.

7) I would like to place the tank and pumping components underneath my existing basement stairs to keep them out of the way. However, that placement provides a volume limitation. Does anyone see any problem with using a horizontal free standing leg tank such as item no. 8810 available at: ? (Cost is about $125)

Another possibly more attractive option would be to use a rectangular open top tank with lid. That would allow easy access to the tank and submersible pumps.

8) Finally, if someone can recommend inexpensive sources for finding any or all of the parts I will need, any input is appreciated.

Sorry for such a long post!

Thanks in advance,

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